Class 10th Science Chapter 11 – Electricity | Potential Difference and Voltage

⚡ Electricity

Potential Difference and Voltage

विभवांतर एवं वोल्टेज

Class 10 Science | CBSE + Foundation + Competitive

⚡ Potential Difference and Voltage

1. Introduction | परिचय

For electric charge to move through a conductor, there must be a difference in electrical potential between two points. This difference is called potential difference.

विद्युत आवेश को एक स्थान से दूसरे स्थान तक प्रवाहित होने के लिए दो बिंदुओं के बीच विद्युत विभव में अंतर होना आवश्यक है। इस अंतर को विभवांतर (Potential Difference) कहते हैं।

Simple Idea:
Potential difference provides the electrical driving force that can cause charge to move through a circuit.

2. What is Potential Difference?

The potential difference between two points is defined as the work done per unit charge in moving a test charge from one point to another.

V = W/Q

Where:

• V = potential difference
• W = work done
• Q = charge moved

3. Meaning of Voltage | वोल्टेज का अर्थ

Voltage is the commonly used term for potential difference. It indicates how much energy is transferred or work is done per unit charge between two points.

Voltage = Energy transferred / Charge

Voltage is a difference between two points. Therefore, saying simply "voltage at one point" can be incomplete unless a reference point is understood.

4. SI Unit of Potential Difference

The SI unit of potential difference is Volt (V).

1 Volt = 1 Joule / 1 Coulomb

Therefore:

1 V = 1 J/C

If 1 joule of work is done in moving 1 coulomb of charge between two points, the potential difference between them is 1 volt.

5. Relation Between Work, Charge and Voltage

From:

V = W/Q

We can obtain:

W = VQ

and:

Q = W/V

Quantity	Formula	SI Unit
Potential difference	V = W/Q	Volt (V)
Work	W = VQ	Joule (J)
Charge	Q = W/V	Coulomb (C)

6. Animated Concept: Voltage as Energy per Charge

7. Potential Difference and Electric Current

Potential difference and electric current are related but they are not the same physical quantity.

Potential Difference	Electric Current
Difference in electric potential between two points	Rate of flow of electric charge
Symbol: V	Symbol: I
Unit: Volt	Unit: Ampere
Measured by voltmeter	Measured by ammeter

8. Role of a Cell in Producing Potential Difference

A cell converts chemical energy into electrical energy and maintains a potential difference between its terminals.

When a conducting path is connected between the terminals, the potential difference can drive charge through the external circuit.

Cell → Potential Difference → Charge Movement → Current

9. Cell, Battery and Voltage

Source	Meaning
Cell	A single electrochemical source that provides a potential difference.
Battery	A combination of cells connected appropriately.

For cells connected in series in the same direction, their voltages can add. The actual terminal voltage of a practical battery can depend on its internal resistance and load.

10. Measuring Potential Difference

Potential difference is measured using a voltmeter.

• Voltmeter is connected in parallel.
• It is connected across the component whose potential difference is required.
• An ideal voltmeter has very high resistance.
• Its high resistance helps minimise the current drawn by the meter.

Memory Trick:
Voltage → Voltmeter → Across the component.

11. Voltmeter Connection Diagram

12. Why is Voltmeter Connected in Parallel?

A voltmeter measures the potential difference between two points. Therefore, its two terminals must be connected to the two points between which the potential difference is to be measured.

Hence it is connected in parallel with the component.

13. What Happens When Voltage Increases?

For a conductor obeying Ohm's law at constant temperature:

I = V/R

If resistance remains constant:

• Voltage increases → Current increases.
• Voltage decreases → Current decreases.

This proportional relationship applies when the resistance remains constant, such as for an ohmic conductor under suitable conditions.

14. Voltage and Resistance

From Ohm's law:

V = IR

Therefore, for fixed current, greater resistance requires greater potential difference.

For fixed resistance, increasing potential difference increases current.

15. Voltage Drop Across a Resistor

When current flows through a resistor, there is a potential difference across it. For an ohmic resistor:

V = IR

This potential difference is often called the voltage drop across the resistor.

16. Potential Difference in Series Circuit

In a series circuit, the total potential difference supplied by the source is distributed among the components.

V = V₁ + V₂ + V₃

The exact voltage across each resistor depends on its resistance.

17. Potential Difference in Parallel Circuit

In a parallel circuit, the potential difference across each branch connected between the same two nodes is the same.

V = V₁ = V₂ = V₃

This is one of the major reasons household appliances are connected in parallel.

18. Potential Difference vs Potential

Potential	Potential Difference
Energy per unit charge relative to a reference	Difference in potential between two points
Depends on reference level	Measured between two points
Can be associated with a point relative to reference	Requires two points

19. Important Numerical Examples

Example 1: 20 J of work is done in moving 5 C charge. Find potential difference.

V = W/Q
V = 20/5
V = 4 V

Example 2: A potential difference of 12 V is applied across a 4 Ω resistor. Find current.

I = V/R
I = 12/4
I = 3 A

Example 3: A current of 2 A flows through a 5 Ω resistor. Find voltage.

V = IR
V = 2 × 5
V = 10 V

Example 4: 60 J of work is done in moving 10 C charge. Find voltage.

V = W/Q
V = 60/10
V = 6 V

Example 5: A 9 V battery transfers 3 C charge. Find work done.

W = VQ
W = 9 × 3
W = 27 J

20. Formula Triangle

    W
   ─────
   V   Q

From this:

V = W/Q

W = VQ

Q = W/V

21. 30 MCQs | बहुविकल्पीय प्रश्न

Q1. Potential difference is defined as:

A. Work done per unit charge

B. Charge per unit time

C. Resistance per unit length

D. Current per unit voltage

Answer: A

Q2. SI unit of potential difference is:

A. Ampere

B. Volt

C. Ohm

D. Coulomb

Answer: B

Q3. The correct formula for potential difference is:

A. V = IR

B. V = Q/t

C. V = W/Q

D. V = R/I

Answer: C

Q4. One volt is equal to:

A. 1 C/J

B. 1 J/A

C. 1 A/C

D. 1 J/C

Answer: D

Q5. Potential difference is measured by:

A. Voltmeter

B. Ammeter

C. Galvanometer only

D. Thermometer

Answer: A

Q6. A voltmeter is connected:

A. In series

B. In parallel

C. Only with the switch

D. Outside the circuit

Answer: B

Q7. A 10 J work moves 2 C charge. Potential difference is:

A. 2 V

B. 10 V

C. 5 V

D. 20 V

Answer: C

Q8. A 5 V potential difference means:

A. 5 J/C

B. 5 C/J

C. 5 J/A

D. 5 A/C

Answer: A

Q9. Which device maintains potential difference in a simple circuit?

A. Switch

B. Cell

C. Ammeter

D. Wire

Answer: B

Q10. Voltage is commonly used as another term for:

A. Current

B. Resistance

C. Potential difference

D. Charge

Answer: C

Q11. The relation between voltage, current and resistance is:

A. V = IR

B. V = I/R

C. V = R/I

D. V = I + R

Answer: A

Q12. If resistance remains constant and voltage doubles, current:

A. Becomes half

B. Doubles

C. Becomes zero

D. Remains unchanged

Answer: B

Q13. The unit of work is:

A. Volt

B. Coulomb

C. Joule

D. Ampere

Answer: C

Q14. The unit of electric charge is:

A. Coulomb

B. Volt

C. Joule

D. Ohm

Answer: A

Q15. Which statement is correct?

A. Voltage and current are identical

B. Voltage is work per unit charge

C. Voltage is charge per unit time

D. Voltage is resistance per unit charge

Answer: B

Q16. In a series circuit, total potential difference is:

A. Always zero

B. Equal to only the first resistor voltage

C. Sum of voltage drops across components

D. Always infinite

Answer: C

Q17. In parallel branches connected across the same two nodes, voltage is:

A. Same

B. Always zero

C. Always different

D. Infinite

Answer: A

Q18. If W = 30 J and Q = 5 C, V equals:

A. 5 V

B. 6 V

C. 10 V

D. 15 V

Answer: B

Q19. If V = 10 V and Q = 4 C, work done is:

A. 2.5 J

B. 10 J

C. 40 J

D. 14 J

Answer: C

Q20. An ideal voltmeter has:

A. Zero resistance

B. Very high resistance

C. Very low voltage

D. Infinite current

Answer: B

Q21. A cell primarily converts:

A. Electrical energy into chemical energy only

B. Chemical energy into electrical energy

C. Heat into mass

D. Light into sound

Answer: B

Q22. Voltage between two points can cause:

A. Charge movement when a conducting path exists

B. Mass to disappear

C. Resistance to become zero automatically

D. No electrical effect ever

Answer: A

Q23. If 1 C charge requires 20 J work, potential difference is:

A. 10 V

B. 20 V

C. 21 V

D. 1/20 V

Answer: B

Q24. If voltage across a 5 Ω resistor is 15 V, current is:

A. 2 A

B. 3 A

C. 5 A

D. 10 A

Answer: B

Q25. Which instrument should not be connected in series for normal voltage measurement?

A. Voltmeter

B. Ammeter

C. Switch

D. Resistor

Answer: A

Q26. The expression W = VQ gives:

A. Current

B. Resistance

C. Work done

D. Resistivity

Answer: C

Q27. Potential difference is a:

A. Difference between potentials at two points

B. Flow of electrons only

C. Type of resistance

D. Unit of current

Answer: A

Q28. If resistance doubles at constant voltage, current becomes:

A. Double

B. Half

C. Four times

D. Unchanged

Answer: B

Q29. The correct dimensional idea of voltage is:

A. Energy per charge

B. Charge per time

C. Charge per resistance

D. Current per charge

Answer: A

Q30. A voltage of 12 V means:

A. 12 C of charge always flows

B. 12 J of energy/work per coulomb

C. 12 A current must always flow

D. Resistance is always 12 Ω

Answer: B

22. 30 Subjective Questions with Answers

2 Marks Q1. Define potential difference.

Potential difference is the work done per unit charge in moving a charge between two points.
V = W/Q

2 Marks Q2. What is the SI unit of potential difference?

Volt (V).

2 Marks Q3. What is voltage?

Voltage is the commonly used term for potential difference between two points.

2 Marks Q4. Define one volt.

One volt is the potential difference when 1 joule of work is done in moving 1 coulomb of charge.
1 V = 1 J/C.

2 Marks Q5. Name the instrument used to measure potential difference.

Voltmeter.

3 Marks Q6. Why is a voltmeter connected in parallel?

Because it measures the potential difference between two points, it must be connected across the component.

3 Marks Q7. Write the relation between work, charge and potential difference.

V = W/Q
Therefore W = VQ.

3 Marks Q8. Differentiate between potential difference and current.

Potential difference is work per unit charge and is measured in volt. Current is rate of flow of charge and is measured in ampere.

3 Marks Q9. What is the role of a cell in a circuit?

A cell provides and maintains a potential difference by converting chemical energy into electrical energy.

3 Marks Q10. What does a 5 V potential difference mean?

It means that 5 joules of work/energy transfer corresponds to each coulomb of charge.

4 Marks Q11. Explain the term potential difference with formula.

Potential difference is work done per unit charge:
V = W/Q.
Its SI unit is volt, where 1 V = 1 J/C.

4 Marks Q12. Explain how a voltmeter is connected in a circuit.

A voltmeter is connected in parallel across the component whose potential difference is to be measured. Its high resistance minimises the current drawn from the circuit.

4 Marks Q13. Explain the difference between voltage and current.

Voltage is potential difference or energy transferred per unit charge. Current is charge flowing per unit time. Their SI units are volt and ampere respectively.

4 Marks Q14. Explain why a cell can produce current in a closed circuit.

The cell maintains a potential difference between its terminals. When a conducting path is completed, this potential difference drives charge through the circuit.

4 Marks Q15. Explain voltage drop across a resistor.

When current passes through a resistor, there is a potential difference across it. For an ohmic resistor, the voltage drop is V = IR.

5 Marks Q16. Derive W = VQ from the definition of potential difference.

Starting with:
V = W/Q
Multiplying both sides by Q:
W = VQ

5 Marks Q17. Explain the significance of 1 volt.

1 volt is the potential difference between two points when 1 joule of work is done to move 1 coulomb of charge between them.

5 Marks Q18. Explain the relationship between voltage, current and resistance.

For an ohmic conductor:
V = IR
Thus, at constant resistance current is directly proportional to voltage. At constant voltage current is inversely proportional to resistance.

5 Marks Q19. Explain potential difference in series and parallel circuits.

In series, source voltage is divided among components:
V = V₁ + V₂ + ...
In parallel, the voltage across each branch is the same:
V = V₁ = V₂ = ...

5 Marks Q20. Why does a voltmeter have high resistance?

High resistance ensures that the voltmeter draws very little current, so it causes minimal disturbance to the circuit being measured.

6 Marks Q21. Explain potential difference using an example.

Suppose 20 J of work is done in moving 5 C charge between two points. Then:
V = W/Q = 20/5 = 4 V.
Thus the potential difference is 4 V, meaning 4 J of work/energy transfer per coulomb.

6 Marks Q22. Explain the working of a voltmeter in a circuit.

A voltmeter compares the electric potential of two points. It is connected in parallel across the component. Its high resistance causes only a very small current to pass through the meter.

6 Marks Q23. A battery provides 12 V to a 6 Ω resistor. Calculate current.

I = V/R
I = 12/6
I = 2 A

6 Marks Q24. A charge of 8 C is moved through a potential difference of 5 V. Find the work done.

W = VQ
W = 5 × 8
W = 40 J

6 Marks Q25. 100 J of work is done in moving 20 C charge. Find voltage.

V = W/Q
V = 100/20
V = 5 V

6 Marks Q26. A resistor carries 3 A current when connected to 12 V. Find resistance.

R = V/I
R = 12/3
R = 4 Ω

6 Marks Q27. Explain why household appliances receive the same supply voltage.

Household appliances are connected in parallel. Each appliance is connected across the same two supply points and therefore receives the same potential difference.

6 Marks Q28. Explain the statement: voltage is energy per unit charge.

From V = W/Q, potential difference tells us how much work or energy transfer corresponds to each coulomb of charge between two points.

6 Marks Q29. Compare a cell and a voltmeter.

A cell is a source that maintains potential difference. A voltmeter is a measuring instrument used to measure potential difference between two points.

6 Marks Q30. Explain all important formulae of potential difference.

• V = W/Q
• W = VQ
• Q = W/V
• V = IR
• I = V/R
• R = V/I

23. Assertion–Reason

Q1. Assertion: A voltmeter is connected in parallel.
Reason: It measures potential difference between two points.

Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

Q2. Assertion: The SI unit of potential difference is volt.
Reason: 1 volt is equal to 1 joule per coulomb.

Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

Q3. Assertion: Increasing voltage across an ohmic resistor increases current.
Reason: At constant resistance, I = V/R.

Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

Q4. Assertion: An ideal voltmeter has very high resistance.
Reason: It should draw very little current from the circuit.

Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

Q5. Assertion: Potential difference and current have the same SI unit.
Reason: Potential difference is measured in volt.

Answer: Assertion is false; Reason is true.

24. HOTS | Higher Order Thinking

HOTS 1. A student says, "A 12 V battery always supplies 12 A current." Is the statement correct?

No. Voltage and current are different quantities. Current depends on the circuit resistance as I = V/R.

HOTS 2. Why does a voltmeter not normally cause a significant change in circuit current?

Because an ideal voltmeter has very high resistance and therefore draws very little current.

HOTS 3. Two resistors are connected in series. Why does the source voltage divide?

The same current flows through both resistors and each produces a voltage drop V = IR. Therefore the source voltage is shared among them.

HOTS 4. A resistor of 10 Ω is connected to 20 V. What happens to current if voltage becomes 40 V while resistance remains unchanged?

I₁ = 20/10 = 2 A.
I₂ = 40/10 = 4 A.
Current doubles.

HOTS 5. Why is voltage called "energy per unit charge"?

Because V = W/Q. It directly represents the work or energy transfer associated with each coulomb of charge.

25. Diagram Labelling Practice

Identify the following in the circuit diagram:

1. Cell / Battery
2. Resistor
3. Voltmeter
4. Connecting wires
5. Positive and negative terminals

Key: The voltmeter must be connected across the component whose potential difference is being measured.

26. CBSE Golden Points ⭐

1. Potential difference is work done per unit charge.
2. V = W/Q.
3. SI unit of potential difference is volt.
4. 1 V = 1 J/C.
5. Voltage is commonly used for potential difference.
6. A cell maintains potential difference between its terminals.
7. Potential difference can drive charge through a conducting path.
8. Voltmeter measures potential difference.
9. Voltmeter is connected in parallel.
10. An ideal voltmeter has very high resistance.
11. For an ohmic conductor, V = IR.
12. In series, source voltage is divided among components.
13. In parallel branches, potential difference is the same.
14. Voltage and current are different physical quantities.
15. Voltage does not by itself specify current; circuit resistance also matters.

27. Memory Tricks 🧠

⚡ Trick 1

Voltage = Work / Charge
V = W/Q

⚡ Trick 2

1 Volt = 1 Joule per Coulomb
1 V = 1 J/C

⚡ Trick 3

Voltmeter → Voltage → Parallel

⚡ Trick 4

V = IR
Voltage = Current × Resistance

⚡ Trick 5

Series → Voltage Divides
Parallel → Voltage Same

28. One-Minute Revision ⚡

⚡ Potential difference = work done per unit charge.

📐 V = W/Q.

🔋 Cell maintains potential difference.

📟 Voltmeter measures voltage.

🔗 Voltmeter is connected in parallel.

📏 1 V = 1 J/C.

⚡ Ohm's law: V = IR.

🔗 Series: voltage divides.

↔️ Parallel: voltage remains same across branches.

🧠 Voltage ≠ Current.

29. Concept Map

🔋 Cell / Battery
↓ ⚡ Potential Difference
↓ 📐 V = W/Q
↓ 🔌 Closed Circuit
↓ ⚡ Current
↓ 🧱 Resistance
↓ 📐 V = IR
↓ 📟 Voltmeter
↓ 🔗 Parallel Connection

30. Final Summary | अंतिम सारांश

Potential difference is the difference in electric potential between two points. It is defined as the work done per unit charge.

V = W/Q

The SI unit is volt:

1 V = 1 J/C

A cell or battery maintains a potential difference that can drive charge through an external conducting circuit.

Potential difference is measured using a voltmeter, which is connected in parallel across the component.

For an ohmic conductor at constant temperature:

V = IR

🔋 Cell → Voltage → Charge Movement → Current

⚡ Electricity

Potential Difference and Voltage

विभवांतर एवं वोल्टेज

Class 10 Science | CBSE + Foundation + Competitive