β‘ Chapter 16: Electricity β Short Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
π What's Inside: This chapter covers electric current, conventional and electronic current, types of current, ammeters and voltmeters, electromotive force, potential difference, Ohm's law, resistance, series and parallel combinations, resistivity, temperature effects, electric power, energy, kilowatt-hour, household wiring, and electrical safety. Each short question is presented with the exact exam-ready answer as per the official PECTAA 2026 Physics curriculum. Perfect for Punjab Boards (Lahore, Gujranwala, Multan, etc.) and all BISE boards across Pakistan.
π Related Resources β Chapter 16: Electricity
π Exercise Short Qs
βοΈ Constructed Response
π Long Questions
π Numerical Problems
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MCQs
Electricity covers electric current, Ohm's law, resistance, series and parallel circuits, electric power, energy, and household wiring. Includes solved examples and numerical problems.
π Quick Jump to Questions
π Short Questions & Answers (PECTAA 2026)
1. What is electricity?
Electricity is the branch of physics that deals with the flow of electric charges.
Electricity is the branch of physics that deals with the flow of electric charges.
2. What is electric current? Write its formula and SI unit.
Amount of charge passing through any cross section of a conductor per unit time is called electric current.
If \(Q\) charge flows in time \(t\), then current \(I\) can be expressed as:
\[I = \frac{Q}{t}\]
Unit: In SI the unit of current is Ampere (A).
Amount of charge passing through any cross section of a conductor per unit time is called electric current.
If \(Q\) charge flows in time \(t\), then current \(I\) can be expressed as:
\[I = \frac{Q}{t}\]
Unit: In SI the unit of current is Ampere (A).
3. Define unit of current.
SI the unit of current is Ampere (A).
Ampere: One ampere is defined as the flow of one coulomb of electric charge per second, which can be written as;
\[1A = 1Cs^{-1}\]
SI the unit of current is Ampere (A).
Ampere: One ampere is defined as the flow of one coulomb of electric charge per second, which can be written as;
\[1A = 1Cs^{-1}\]
4. What is conventional current?
Before the discovery of electrons, the electric current was considered to be due to flow of positive charges, named as Conventional Current. These charges move from positive terminal to the negative terminal of the power source.
OR
Conventional current is the flow of positive charge from the positive terminal to the negative terminal of a source of electricity.
Before the discovery of electrons, the electric current was considered to be due to flow of positive charges, named as Conventional Current. These charges move from positive terminal to the negative terminal of the power source.
OR
Conventional current is the flow of positive charge from the positive terminal to the negative terminal of a source of electricity.
5. What is electronic current?
After the discovery of electrons, the electric current was described due to the movement of electrons which was named as electronic current. The movement of electrons in one direction corresponds to the movement of positive charges in opposite direction.
OR
Electronic current is the flow of electrons from the negative terminal to the positive terminal of a source.
After the discovery of electrons, the electric current was described due to the movement of electrons which was named as electronic current. The movement of electrons in one direction corresponds to the movement of positive charges in opposite direction.
OR
Electronic current is the flow of electrons from the negative terminal to the positive terminal of a source.
6. How is electric current produced in metallic conductors and electrolytes?
Electric current is produced differently in metallic conductors and electrolytes:
In metallic conductors, electric current is produced due to the movement of free electrons.
In electrolytes, electric current is produced due to the movement of both positive and negative ions.
Electric current is produced differently in metallic conductors and electrolytes:
In metallic conductors, electric current is produced due to the movement of free electrons.
In electrolytes, electric current is produced due to the movement of both positive and negative ions.
7. What are the types of electric current?
There are two types of electric current:
1. Direct Current (D.C.)
2. Alternating Current (A.C.)
Direct Current (D.C.): Direct Current is an electrical current in which the electric charge flows in one direction only.
In a D.C. circuit, the voltage remains constant over time, and the strength of the current does not change.
For example, current supplied by a battery.
Alternating Current (A.C.): Alternating Current is a type of current that periodically reverses its direction.
A.C. changes direction every \(\frac{1}{50}\) second, and its frequency is 50 hertz (Hz).
For example, electricity produced by power stations.
There are two types of electric current:
1. Direct Current (D.C.)
2. Alternating Current (A.C.)
Direct Current (D.C.): Direct Current is an electrical current in which the electric charge flows in one direction only.
In a D.C. circuit, the voltage remains constant over time, and the strength of the current does not change.
For example, current supplied by a battery.
Alternating Current (A.C.): Alternating Current is a type of current that periodically reverses its direction.
A.C. changes direction every \(\frac{1}{50}\) second, and its frequency is 50 hertz (Hz).
For example, electricity produced by power stations.
8. Why is A.C preferred over D.C? OR What is the advantage of A.C over D.C
Alternating current is preferred because it can be transmitted over long distances with very little power loss.
Alternating current is preferred because it can be transmitted over long distances with very little power loss.
9. What is an ammeter? How is an ammeter connected in a circuit?
An ammeter is a device used to measure the current flowing through a circuit.
An ammeter is connected in series with the circuit so that the entire current passes through it.
An ammeter is a device used to measure the current flowing through a circuit.
An ammeter is connected in series with the circuit so that the entire current passes through it.
10. What are the two main types of ammeters?
The two main types of ammeters are:
i. Analog ammeter
ii. Digital ammeter
Analog Ammeter: An analog ammeter measures electric current by using a moving pointer (needle) that indicates the current on a calibrated scale.
Digital Ammeter: A digital ammeter measures electric current and displays the reading directly in numerical form on a digital screen.
The two main types of ammeters are:
i. Analog ammeter
ii. Digital ammeter
Analog Ammeter: An analog ammeter measures electric current by using a moving pointer (needle) that indicates the current on a calibrated scale.
Digital Ammeter: A digital ammeter measures electric current and displays the reading directly in numerical form on a digital screen.
11. How does an analog ammeter work?
An analog ammeter uses a needle and scale to indicate the current. The current flowing through the circuit generates a magnetic field that moves the needle on the scale. The scale usually has multiple ranges, and the correct range must be selected depending on the expected current.
An analog ammeter uses a needle and scale to indicate the current. The current flowing through the circuit generates a magnetic field that moves the needle on the scale. The scale usually has multiple ranges, and the correct range must be selected depending on the expected current.
12. How does a digital ammeter work?
A digital ammeter provides a numerical reading of the current on a digital display. It offers more precision compared to an analog ammeter. Digital ammeters also come with various ranges, and some automatically adjust the range depending on the detected current.
A digital ammeter provides a numerical reading of the current on a digital display. It offers more precision compared to an analog ammeter. Digital ammeters also come with various ranges, and some automatically adjust the range depending on the detected current.
13. What is electromotive force (e.m.f.)?
Electromotive force is the electric potential energy supplied by a battery to a unit positive charge when it flows through the closed circuit.
\[e.m.f = \frac{Energy}{Charge}\]
\[E = \frac{W}{Q}\]
The SI unit of electromotive force is the volt (V).
Electromotive force is the electric potential energy supplied by a battery to a unit positive charge when it flows through the closed circuit.
\[e.m.f = \frac{Energy}{Charge}\]
\[E = \frac{W}{Q}\]
The SI unit of electromotive force is the volt (V).
14. What is one volt (V)?
One volt (V) is defined as one joule of energy per coulomb of charge.
\[1V = 1JC^{-1}\]
This means that if 1 joule of energy is used to move 1 coulomb of charge, the voltage is 1 volt.
One volt (V) is defined as one joule of energy per coulomb of charge.
\[1V = 1JC^{-1}\]
This means that if 1 joule of energy is used to move 1 coulomb of charge, the voltage is 1 volt.
15. What is potential difference?
Electric potential (V) is the amount of electric potential energy (W) per unit charge (Q) at a specific point in an electric field.
\[V = \frac{W}{Q}\]
The SI unit of potential difference is the volt (V).
Electric potential (V) is the amount of electric potential energy (W) per unit charge (Q) at a specific point in an electric field.
\[V = \frac{W}{Q}\]
The SI unit of potential difference is the volt (V).
16. What creates potential difference in a battery?
A chemical reaction inside the battery causes a buildup of electrons at the negative terminal and a shortage of electrons at the positive terminal. This imbalance creates a potential difference between the two terminals.
A chemical reaction inside the battery causes a buildup of electrons at the negative terminal and a shortage of electrons at the positive terminal. This imbalance creates a potential difference between the two terminals.
17. What is a voltmeter?
A voltmeter is an instrument used to measure the potential difference (voltage) between two points in an electric circuit.
OR
Voltage can be measured using a device called voltmeter.
A voltmeter is an instrument used to measure the potential difference (voltage) between two points in an electric circuit.
OR
Voltage can be measured using a device called voltmeter.
18. What are the types of voltmeters?
Voltmeters are of two types: analog and digital.
Both are available in different ranges to measure different values of voltage.
An analog voltmeter shows the voltage using a needle moving over a scale, while a digital voltmeter displays the voltage as a numerical value on a screen.
Voltmeters are of two types: analog and digital.
Both are available in different ranges to measure different values of voltage.
An analog voltmeter shows the voltage using a needle moving over a scale, while a digital voltmeter displays the voltage as a numerical value on a screen.
19. What is the total e.m.f. when multiple sources are connected in series?
When multiple voltage sources (e.g., batteries) are connected in series, their total electromotive force (e.m.f.) is simply the sum of their individual e.m.f.
This is because the voltage sources add energy to the charges one after the other.
\[E_{total} = E_{1} + E_{2} + E_{3} + \dots + E_{n}\]
When multiple voltage sources (e.g., batteries) are connected in series, their total electromotive force (e.m.f.) is simply the sum of their individual e.m.f.
This is because the voltage sources add energy to the charges one after the other.
\[E_{total} = E_{1} + E_{2} + E_{3} + \dots + E_{n}\]
20. What is the e.m.f. of identical sources connected in parallel?
When identical voltage sources (such as batteries with the same voltage) are connected in parallel, the total electromotive force (e.m.f.) remains equal to the e.m.f. of a single source.
This is because each battery is connected across the same two points, so the voltage does not change.
However, the total current increases because each source supplies current independently.
\[E_{total} = E_{1} = E_{2} = E_{3} = \dots = E_{n}\]
When identical voltage sources (such as batteries with the same voltage) are connected in parallel, the total electromotive force (e.m.f.) remains equal to the e.m.f. of a single source.
This is because each battery is connected across the same two points, so the voltage does not change.
However, the total current increases because each source supplies current independently.
\[E_{total} = E_{1} = E_{2} = E_{3} = \dots = E_{n}\]
21. State Ohm's law also write mathematical form.
The current flowing through a conductor is directly proportional to the potential difference V across its two ends of a conductor, provided the physical state (dimension, temperature, etc.) of the conductor remains same. Mathematically
\[I \propto V\]
\[V \propto I\]
\[V = IR\]
where R is the constant of proportionality, and is the resistance of the conductors.
The current flowing through a conductor is directly proportional to the potential difference V across its two ends of a conductor, provided the physical state (dimension, temperature, etc.) of the conductor remains same. Mathematically
\[I \propto V\]
\[V \propto I\]
\[V = IR\]
where R is the constant of proportionality, and is the resistance of the conductors.
22. What is the SI unit of resistance?
The SI unit of resistance is the ohm (Ξ©).
\[1 Ξ© = 1 VA^{-1}\]
where 1 ohm is the resistance of a conductor when a potential difference of 1 volt produces a current of 1 ampere.
The SI unit of resistance is the ohm (Ξ©).
\[1 Ξ© = 1 VA^{-1}\]
where 1 ohm is the resistance of a conductor when a potential difference of 1 volt produces a current of 1 ampere.
23. What is a series combination of resistors? Also write its formula for equivalent resistance.
When resistors are connected in such a way that there is only one path for the current to flow, then it is called series combination of resistors.
Equivalent resistance is equal to the sum of individual resistances.
\[R_{e} = R_{1} + R_{2} + R_{3}\]
When resistors are connected in such a way that there is only one path for the current to flow, then it is called series combination of resistors.
Equivalent resistance is equal to the sum of individual resistances.
\[R_{e} = R_{1} + R_{2} + R_{3}\]
24. What is a parallel combination of resistors? Also write its formula for equivalent resistance.
When there are multiple paths for current flow in a circuit, the combination of resistances is referred to as parallel combination.
The reciprocal of equivalent resistance is equal to the sum of reciprocals of individual resistances.
\[\frac{1}{R_e} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}\]
When there are multiple paths for current flow in a circuit, the combination of resistances is referred to as parallel combination.
The reciprocal of equivalent resistance is equal to the sum of reciprocals of individual resistances.
\[\frac{1}{R_e} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}\]
25. Why can birds sit safely on electric wires?
Birds are safe because both their feet touch the same potential wire. There is no voltage difference, so no current flows through their bodies.
Birds are safe because both their feet touch the same potential wire. There is no voltage difference, so no current flows through their bodies.
26. What is resistance?
The opposition to the flow of electric current is called resistance.
The opposition to the flow of electric current is called resistance.
27. On which factors does the resistance of a conductor depend?
The resistance of a conductor:
β’ is directly proportional to its length (L).
β’ is inversely proportional to its cross-sectional area (A).
Mathematically,
\[R \propto L\]
\[R \propto \frac{1}{A}\]
\[\Rightarrow R \propto \frac{L}{A}\]
\[R = \rho \frac{L}{A}\]
The resistance of a conductor:
β’ is directly proportional to its length (L).
β’ is inversely proportional to its cross-sectional area (A).
Mathematically,
\[R \propto L\]
\[R \propto \frac{1}{A}\]
\[\Rightarrow R \propto \frac{L}{A}\]
\[R = \rho \frac{L}{A}\]
28. What is electrical resistivity? Write its SI unit.
Electrical resistivity (Ο) is a property of a material that indicates how strongly it resists the flow of electric current.
The SI unit of resistivity is ohm-metre (Ξ©m).
Note: Materials with high resistivity are poor conductors of electricity, whereas materials with low resistivity are good conductors.
Electrical resistivity (Ο) is a property of a material that indicates how strongly it resists the flow of electric current.
The SI unit of resistivity is ohm-metre (Ξ©m).
Note: Materials with high resistivity are poor conductors of electricity, whereas materials with low resistivity are good conductors.
29. What is the effect of temperature on the resistance of a conductor?
The resistance and resistivity of a conductor change with temperature. In most conductors (metals), resistance increases with an increase in temperature because the increased vibration of atoms makes it more difficult for electrons to flow.
For example, in a filament lamp, the resistance of the filament increases as its temperature increases.
The resistance and resistivity of a conductor change with temperature. In most conductors (metals), resistance increases with an increase in temperature because the increased vibration of atoms makes it more difficult for electrons to flow.
For example, in a filament lamp, the resistance of the filament increases as its temperature increases.
30. What is the effect of temperature on the resistance of semiconductors?
In semiconductors, resistance decreases as the temperature increases. This is because an increase in temperature releases more free charge carriers, which increases conductivity and reduces resistance.
For example, a thermistor is a semiconductor whose resistance decreases with an increase in temperature.
In semiconductors, resistance decreases as the temperature increases. This is because an increase in temperature releases more free charge carriers, which increases conductivity and reduces resistance.
For example, a thermistor is a semiconductor whose resistance decreases with an increase in temperature.
31. What is a thermistor?
Thermistor, which is made up of a semiconductor material, is a type of resistor whose resistance decreases as its temperature increases.
Thermistor, which is made up of a semiconductor material, is a type of resistor whose resistance decreases as its temperature increases.
32. What is a potential divider circuit?
A potential or voltage divider is a circuit that divides a voltage into smaller parts using resistors. It consists of two or more resistors connected in series across a voltage source. The voltage across each resistor is proportional to its resistance relative to the total resistance of the circuit.
A potential or voltage divider is a circuit that divides a voltage into smaller parts using resistors. It consists of two or more resistors connected in series across a voltage source. The voltage across each resistor is proportional to its resistance relative to the total resistance of the circuit.
33. What is the formula for the potential divider?
For two resistors \(R_{1}\) and \(R_{2}\) connected in series,
\[\frac{R_1}{R_2} = \frac{V_1}{V_2}\]
The total voltage is:
The voltage across resistor \(R_{1}\) is:
\[V_{1} = IR_{1}\]
\[V_{1} = \frac{V_{total}}{R_{e}}\times R_{1} \quad \because I = \frac{V}{R}\]
\[V_{1} = V_{total}\times \frac{R_{1}}{R_{e}}\]
Similarly
\[V_{2} = V_{total}\times \frac{R_{2}}{R_{1} + R_{2}}\]
For two resistors \(R_{1}\) and \(R_{2}\) connected in series,
\[\frac{R_1}{R_2} = \frac{V_1}{V_2}\]
The total voltage is:
The voltage across resistor \(R_{1}\) is:
\[V_{1} = IR_{1}\]
\[V_{1} = \frac{V_{total}}{R_{e}}\times R_{1} \quad \because I = \frac{V}{R}\]
\[V_{1} = V_{total}\times \frac{R_{1}}{R_{e}}\]
Similarly
\[V_{2} = V_{total}\times \frac{R_{2}}{R_{1} + R_{2}}\]
34. What is the resistor colour code system?
Resistor colour codes are a system of coloured bands printed on resistors to indicate their resistance value and tolerance. In this way, a resistor's value can be identified without using a multimeter.
Resistor colour codes are a system of coloured bands printed on resistors to indicate their resistance value and tolerance. In this way, a resistor's value can be identified without using a multimeter.
35. What is meant by tolerance in resistor colour codes?
Tolerance means how much a resistor's actual value can be different from the value written on it.
Tolerance means how much a resistor's actual value can be different from the value written on it.
36. What do the four bands of a resistor indicate?
In a four-band resistor:
i. The first and second bands indicate the first and second digits.
ii. The third band indicates the multiplier.
iii. The fourth band indicates the tolerance.
In a four-band resistor:
i. The first and second bands indicate the first and second digits.
ii. The third band indicates the multiplier.
iii. The fourth band indicates the tolerance.
37. Explain the colour code of a resistor having Red, Violet, Yellow, and Gold bands.
For a resistor with Red, Violet, Yellow, and Gold bands:
Red \(= 2\)
Violet \(= 7\)
Yellow \(=\) Multiplier \((10^{4})\)
Gold \(=\) Tolerance \((\pm 5\%)\)
Therefore,
\[Resistance = 27\times 10^{4}\Omega\]
\[= 270000\Omega\]
\[= 270\times 10^{3}\Omega\]
\[= 270k\Omega\]
For a resistor with Red, Violet, Yellow, and Gold bands:
Red \(= 2\)
Violet \(= 7\)
Yellow \(=\) Multiplier \((10^{4})\)
Gold \(=\) Tolerance \((\pm 5\%)\)
Therefore,
\[Resistance = 27\times 10^{4}\Omega\]
\[= 270000\Omega\]
\[= 270\times 10^{3}\Omega\]
\[= 270k\Omega\]
38. What is a Negative Temperature Coefficient (NTC) thermistor?
A Negative Temperature Coefficient (NTC) thermistor is a type of resistor whose resistance decreases as the temperature increases. This is because the increase in temperature gives more energy to the charge carriers, allowing them to move more freely through the material and reducing the resistance.
A Negative Temperature Coefficient (NTC) thermistor is a type of resistor whose resistance decreases as the temperature increases. This is because the increase in temperature gives more energy to the charge carriers, allowing them to move more freely through the material and reducing the resistance.
39. What is the action of an NTC thermistor?
As the temperature increases, the resistance of an NTC thermistor decreases. Therefore, it is useful for detecting changes in temperature.
As the temperature increases, the resistance of an NTC thermistor decreases. Therefore, it is useful for detecting changes in temperature.
40. What are the applications of an NTC thermistor?
An NTC thermistor is used in:
i. Temperature sensors in electronic devices.
ii. Temperature monitoring and compensation circuits.
iii. Over-current protection in power supplies.
An NTC thermistor is used in:
i. Temperature sensors in electronic devices.
ii. Temperature monitoring and compensation circuits.
iii. Over-current protection in power supplies.
41. What is a Light-Dependent Resistor (LDR)?
A Light-Dependent Resistor (LDR) is a type of resistor whose resistance decreases as the intensity of light increases. The more light that falls on the LDR, the more current flows through it because its resistance decreases.
A Light-Dependent Resistor (LDR) is a type of resistor whose resistance decreases as the intensity of light increases. The more light that falls on the LDR, the more current flows through it because its resistance decreases.
42. What is the action of a Light-Dependent Resistor (LDR)?
As the light intensity increases, the resistance of an LDR decreases, allowing more current to pass through. Therefore, LDRs are widely used in light-sensing circuits where changes in light intensity are monitored.
As the light intensity increases, the resistance of an LDR decreases, allowing more current to pass through. Therefore, LDRs are widely used in light-sensing circuits where changes in light intensity are monitored.
43. What are the applications of a Light-Dependent Resistor (LDR)?
Light-Dependent Resistor (LDR) is used in:
i. Street lighting that automatically turns ON when it gets dark.
ii. Brightness sensors in cameras that adjust exposure according to the ambient light level.
Light-Dependent Resistor (LDR) is used in:
i. Street lighting that automatically turns ON when it gets dark.
ii. Brightness sensors in cameras that adjust exposure according to the ambient light level.
44. What are the common uses of electricity?
The common uses of electricity are:
1. Heating: It is used in electric heaters, stoves, and water heaters.
2. Lighting: It is used in electric bulbs, streetlights, and flashlights.
3. Battery Charging: It is used to charge mobile phones, laptops, electric vehicles, and other portable devices.
4. Powering Motors: It is used in washing machines, refrigerators, industrial machinery, electric cars, and trains.
5. Electronic Systems: It is used to operate computers, televisions, smartphones, and other electronic devices.
The common uses of electricity are:
1. Heating: It is used in electric heaters, stoves, and water heaters.
2. Lighting: It is used in electric bulbs, streetlights, and flashlights.
3. Battery Charging: It is used to charge mobile phones, laptops, electric vehicles, and other portable devices.
4. Powering Motors: It is used in washing machines, refrigerators, industrial machinery, electric cars, and trains.
5. Electronic Systems: It is used to operate computers, televisions, smartphones, and other electronic devices.
45. What is electric power? Write its SI unit.
Electric power is the rate at which electrical energy is transferred or consumed in a circuit. It measures how quickly work is done or energy is used.
\[P = \frac{W}{t}\]
SI Unit: The unit of electric power is watt which is equal to one joule per second.
\[1W = Js^{-1}\]
Electric power is the rate at which electrical energy is transferred or consumed in a circuit. It measures how quickly work is done or energy is used.
\[P = \frac{W}{t}\]
SI Unit: The unit of electric power is watt which is equal to one joule per second.
\[1W = Js^{-1}\]
46. Write the formula for electric power.
Electric power is equal to the product of current and voltage.
\[P = IV\]
Electric power is equal to the product of current and voltage.
\[P = IV\]
47. Prove \(P = \frac{V^2}{R}\)
We know that
\[P = \frac{W}{t}\]
\[P = \frac{QV}{t}\]
\[P = \left(\frac{Q}{t}\right)V\]
\[P = IV\]
\[P = \left(\frac{V}{R}\right)V\]
\[P = \frac{V^2}{R}\]
\[P = \frac{V^2}{R}\]
We know that
\[P = \frac{W}{t}\]
\[P = \frac{QV}{t}\]
\[P = \left(\frac{Q}{t}\right)V\]
\[P = IV\]
\[P = \left(\frac{V}{R}\right)V\]
\[P = \frac{V^2}{R}\]
\[P = \frac{V^2}{R}\]
48. Prove that \(P = I^2 R\)
We know that
\[P = \frac{W}{t}\]
\[P = \frac{QV}{t}\]
\[P = \left(\frac{Q}{t}\right)V\]
\[P = IV\]
\[P = I(IR)\]
\[P = I^2 R\]
We know that
\[P = \frac{W}{t}\]
\[P = \frac{QV}{t}\]
\[P = \left(\frac{Q}{t}\right)V\]
\[P = IV\]
\[P = I(IR)\]
\[P = I^2 R\]
49. What is Joule's law?
The heat energy produced in a resistance is equal to the product of square of the current, resistance and time. Mathematically;
\[H = I^2 Rt\]
The heat energy produced in a resistance is equal to the product of square of the current, resistance and time. Mathematically;
\[H = I^2 Rt\]
50. What is the relationship between electric power and heat energy?
The total heat energy produced is equal to the product of electric power and time.
\[H = Pt\]
This shows that the power of a resistor determines how quickly heat is produced.
The total heat energy produced is equal to the product of electric power and time.
\[H = Pt\]
This shows that the power of a resistor determines how quickly heat is produced.
51. What is a kilowatt-hour (kWh)?
The amount of energy delivered by a power of one kilowatt in one hour is called one kilowatt-hour.
\[1kWh = 3.6MJ\]
Note: A kilowatt-hour (kWh) is the unit used to measure large amounts of electrical energy.
The amount of energy delivered by a power of one kilowatt in one hour is called one kilowatt-hour.
\[1kWh = 3.6MJ\]
Note: A kilowatt-hour (kWh) is the unit used to measure large amounts of electrical energy.
52. Convert 1 kWh into Joules.
\[1kWh = 1000Wh\]
\[1kWh = (1000W)(3600s)\]
\[1kWh = 3600000J\]
\[1kWh = 3.6\times 10^{6}J\]
\[1kWh = 3.6MJ\]
\[1kWh = 1000Wh\]
\[1kWh = (1000W)(3600s)\]
\[1kWh = 3600000J\]
\[1kWh = 3.6\times 10^{6}J\]
\[1kWh = 3.6MJ\]
53. Write the formula for electrical energy in kilowatt-hour.
\[Electrical\ Energy(kWh) = \frac{Power(W)\times time(h)}{1000}\]
\[Electrical\ Energy(kWh) = \frac{Power(W)\times time(h)}{1000}\]
54. How is the cost of electricity calculated?
The cost of electricity is calculated by:
\[Cost = Number\ of\ units\ consumed \times Cost\ of\ one\ unit\]
\[Cost = \frac{Power(W)\times time(h)}{1000} \times Cost\ of\ one\ unit\]
The cost of electricity is calculated by:
\[Cost = Number\ of\ units\ consumed \times Cost\ of\ one\ unit\]
\[Cost = \frac{Power(W)\times time(h)}{1000} \times Cost\ of\ one\ unit\]
55. What does an electric meter measure?
The electric meter installed in our houses measures the consumption of electrical energy in kilowatt-hours (kWh), according to which we pay our electricity bills.
Note: Power bills measure energy, not electricity. Electricity bills show the amount of electrical energy consumed in kilowatt-hours (kWh), not the amount of electricity consumed.
The electric meter installed in our houses measures the consumption of electrical energy in kilowatt-hours (kWh), according to which we pay our electricity bills.
Note: Power bills measure energy, not electricity. Electricity bills show the amount of electrical energy consumed in kilowatt-hours (kWh), not the amount of electricity consumed.
56. Why are household appliances connected in parallel?
Household appliances are connected in parallel so that each appliance gets its own direct connection to the power supply and works independently. If one appliance is switched OFF or becomes faulty, the other appliances continue to operate normally.
Household appliances are connected in parallel so that each appliance gets its own direct connection to the power supply and works independently. If one appliance is switched OFF or becomes faulty, the other appliances continue to operate normally.
57. What are the advantages of a parallel circuit in household wiring?
The advantages of a parallel circuit are:
i. Each appliance receives the same supply voltage.
ii. Each appliance works independently.
iii. If one appliance or fuse fails, the other appliances continue to work.
iv. It is safer and more reliable.
The advantages of a parallel circuit are:
i. Each appliance receives the same supply voltage.
ii. Each appliance works independently.
iii. If one appliance or fuse fails, the other appliances continue to work.
iv. It is safer and more reliable.
58. What are the common electrical hazards?
Common electrical hazards include:
i. Damaged insulation
ii. Overheating of cables
iii. Overloading of circuits
These hazards may cause electric shocks, short circuits, or fires.
Common electrical hazards include:
i. Damaged insulation
ii. Overheating of cables
iii. Overloading of circuits
These hazards may cause electric shocks, short circuits, or fires.
59. What is the function of a fuse?
A fuse is a safety device that contains a thin wire which melts when excessive current flows through it. As a result, the circuit breaks and the flow of electricity stops.
A fuse is a safety device that contains a thin wire which melts when excessive current flows through it. As a result, the circuit breaks and the flow of electricity stops.
60. What is the function of a trip switch (circuit breaker)?
A trip switch (circuit breaker) is a safety device that automatically switches OFF the power when it detects a fault such as overloading or a short circuit.
A trip switch (circuit breaker) is a safety device that automatically switches OFF the power when it detects a fault such as overloading or a short circuit.
61. What is the function of the earth wire?
The earth wire provides a low-resistance path for fault current to flow safely into the ground. This prevents electric shock and causes the fuse or trip switch to disconnect the power supply.
The earth wire provides a low-resistance path for fault current to flow safely into the ground. This prevents electric shock and causes the fuse or trip switch to disconnect the power supply.
62. Name the three wires of a household main circuit.
A household main circuit consists of:
1. Live (Line) wire - carries current from the power supply.
2. Neutral wire - completes the circuit.
3. Earth wire - provides a safety path for fault current.
A household main circuit consists of:
1. Live (Line) wire - carries current from the power supply.
2. Neutral wire - completes the circuit.
3. Earth wire - provides a safety path for fault current.
63. Why are electrical appliances earthed or double-insulated?
Electrical appliances are earthed or double-insulated to protect users from electric shock. Appliances with metal casings are connected to the earth wire, whereas double-insulated appliances have plastic casings, which do not conduct electricity.
Electrical appliances are earthed or double-insulated to protect users from electric shock. Appliances with metal casings are connected to the earth wire, whereas double-insulated appliances have plastic casings, which do not conduct electricity.
64. What are the harmful effects of electric shock?
An electric shock can:
i. Cause burns at the entry and exit points.
ii. Lead to cardiorespiratory failure.
iii. Cause seizures.
An electric shock can:
i. Cause burns at the entry and exit points.
ii. Lead to cardiorespiratory failure.
iii. Cause seizures.
π Key Formulas β Electricity
Electric Current: \( I = \frac{Q}{t} \)
Ohm's Law: \( V = IR \)
Series Resistance: \( R_e = R_1 + R_2 + R_3 \)
Parallel Resistance: \( \frac{1}{R_e} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \)
Electric Power: \( P = IV = I^2R = \frac{V^2}{R} \)
Electrical Energy: \( E = Pt \)
Resistivity: \( R = \rho \frac{L}{A} \)
Unit 10Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14Light
Unit 15Electrostatics
Unit 16β¨ Electricity
Unit 17Electromagnetism
Unit 18Electromagnetic Induction & EM Waves
Unit 19Electronics
Unit 20Atomic and Nuclear Physics
Unit 21Space and Environment
π Complete syllabus coverage for Class 10 Physics (PECTAA 2026) β Units 10 to 21
π‘ Exam Tip:
For board exams, define key terms precisely, mention formulas with units, and relate to real-life examples. These questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus