Class 10th Science Chapter 11 – Electricity | Electric Current and Electric Circuit

⚡ Electricity

Electric Current and Electric Circuit

विद्युत धारा एवं विद्युत परिपथ

Class 10 Science | CBSE + Foundation + Competitive

⚡ Electric Current and Electric Circuit

1. Introduction | परिचय

Electricity is one of the most important forms of energy used in modern life. Electrical appliances work because electric charges can move through a suitable conducting path.

Electric current is the rate of flow of electric charge through a conductor.

विद्युत धारा किसी चालक के अनुप्रस्थ काट से होकर प्रति इकाई समय में प्रवाहित होने वाले विद्युत आवेश की मात्रा है।

I = Q / t

where:

• I = electric current
• Q = electric charge
• t = time

2. Electric Charge | विद्युत आवेश

Electric charge is a fundamental property of matter responsible for electrical interactions.

There are two types of electric charge:

• Positive charge
• Negative charge

1 Coulomb = approximately 6.25 × 10¹⁸ electrons

SI unit of charge: Coulomb (C)

3. Electric Current | विद्युत धारा

Electric current is the rate of flow of electric charge.

I = Q/t

The SI unit of electric current is Ampere (A).

If 1 coulomb of charge flows through a conductor in 1 second, the current is 1 ampere.

1 A = 1 C/s

4. Direction of Electric Current | विद्युत धारा की दिशा

By convention, electric current is considered to flow from the positive terminal to the negative terminal of a source through the external circuit.

In metallic conductors, electrons actually drift from the negative terminal toward the positive terminal.

Current	Electron motion
Conventional current: + → −	Electrons: − → +

Important: Do not confuse conventional current direction with electron drift direction.

5. Electric Circuit | विद्युत परिपथ

An electric circuit is a continuous conducting path through which electric current can flow.

A simple electric circuit generally contains:

• Electric cell or battery
• Connecting wires
• Switch/key
• Electrical load such as bulb

6. Animated Electric Circuit Diagram

7. Closed and Open Circuit

Closed Circuit	Open Circuit
Complete conducting path	Broken/incomplete path
Current flows	Current does not flow
Bulb can glow	Bulb does not glow
Switch closed	Switch open

8. Potential Difference | विभवांतर

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

V = W/Q

where:

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

SI unit of potential difference is Volt (V).

1 V = 1 J/C

9. Role of Cell/Battery

A cell converts chemical energy into electrical energy and provides a potential difference that can drive charge through an external circuit.

A battery is a combination of two or more cells connected appropriately.

Cell	Battery
Single electrochemical source	Combination of cells
Usually provides a specified potential difference	Can provide greater voltage depending on connection

10. Ammeter | एमीटर

An ammeter is used to measure electric current in a circuit.

• Unit: Ampere (A)
• It is connected in series.
• Its resistance is designed to be very small.

Memory Trick:
Ammeter → Ampere → Always in series

11. Voltmeter | वोल्टमीटर

A voltmeter measures potential difference between two points.

• Unit: Volt (V)
• It is connected in parallel.
• It has very high resistance.

Memory Trick:
Voltmeter → Voltage → Across the component

12. Resistance | प्रतिरोध

Resistance is the property of a conductor that opposes the flow of electric charge.

R = V/I

SI unit of resistance is Ohm (Ω).

1 Ω = 1 V/A

13. Ohm's Law | ओम का नियम

According to Ohm's law, at constant temperature, the potential difference across a conductor is directly proportional to the current through it.

V ∝ I

Therefore:

V = IR

14. V-I Relationship

For an ohmic conductor at constant temperature, a graph of V against I is a straight line passing through the origin.

Slope of V-I graph = R

15. Factors Affecting Resistance

Resistance of a uniform conductor depends on:

• Length (L)
• Area of cross-section (A)
• Nature of material / resistivity (ρ)
• Temperature

R = ρL/A

Change	Effect on R
Length increases	Resistance increases
Area increases	Resistance decreases
Length decreases	Resistance decreases
Area decreases	Resistance increases

16. Resistivity | प्रतिरोधकता

Resistivity is a property of a material that indicates how strongly the material resists the flow of electric current.

ρ = RA/L

SI unit of resistivity is Ω m.

Resistivity depends on the nature of material and temperature, not directly on the dimensions of a particular sample.

17. Resistors in Series | श्रेणी क्रम

When resistors are connected one after another in a single path, they are said to be connected in series.

R = R₁ + R₂ + R₃

In series:

• Same current flows through each resistor.
• Total resistance is greater than any individual resistance.
• Potential difference is divided among resistors.

18. Resistors in Parallel | समानांतर क्रम

In a parallel connection, current has more than one path.

1/R = 1/R₁ + 1/R₂ + 1/R₃

In parallel:

• Potential difference across each branch is the same.
• Current divides among different branches.
• Equivalent resistance is less than the smallest individual resistance.

20. Why Are Household Appliances Connected in Parallel?

• Each appliance receives the same supply voltage.
• Each appliance can be operated independently.
• If one appliance fails, others can continue working.
• Different appliances can draw different currents according to their resistance/power.

21. Important Numerical Examples

Example 1: A charge of 20 C flows through a conductor in 5 s. Find current.

I = Q/t
I = 20/5
I = 4 A

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

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

Example 3: A resistor carries 2 A current when connected to 10 V. Find resistance.

R = V/I
R = 10/2
R = 5 Ω

Example 4: Two resistors 4 Ω and 6 Ω are connected in series. Find equivalent resistance.

R = R₁ + R₂
R = 4 + 6
R = 10 Ω

Example 5: Two resistors 6 Ω and 3 Ω are connected in parallel. Find equivalent resistance.

1/R = 1/6 + 1/3
1/R = 1/6 + 2/6
1/R = 3/6 = 1/2
R = 2 Ω

22. Important SI Units

Quantity	Symbol	SI Unit
Charge	Q	Coulomb (C)
Current	I	Ampere (A)
Potential difference	V	Volt (V)
Resistance	R	Ohm (Ω)
Resistivity	ρ	Ω m
Work/Energy	W/E	Joule (J)

23. 30 MCQs | बहुविकल्पीय प्रश्न

Q1. Electric current is defined as:

A. Rate of flow of electric charge

B. Rate of flow of mass

C. Amount of resistance

D. Electrical energy only

Answer: A

Q2. SI unit of electric current is:

A. Volt

B. Ampere

C. Ohm

D. Coulomb

Answer: B

Q3. The formula for current is:

A. I = V/R

B. I = R/V

C. I = Q/t

D. I = WQ

Answer: C

Q4. Potential difference is measured in:

A. Ampere

B. Coulomb

C. Ohm

D. Volt

Answer: D

Q5. An ammeter is connected:

A. In series

B. In parallel

C. Across the battery only

D. Outside the circuit

Answer: A

Q6. A voltmeter is connected:

A. In series

B. In parallel

C. In the switch only

D. Nowhere

Answer: B

Q7. Ohm's law is:

A. P = VI

B. R = ρL/A

C. V = IR

D. Q = It

Answer: C

Q8. SI unit of resistance is:

A. Ampere

B. Volt

C. Watt

D. Ohm

Answer: D

Q9. Conventional current flows externally from:

A. Positive to negative terminal

B. Negative to positive terminal

C. Both directions equally

D. Earth to battery

Answer: A

Q10. Electrons in a metallic conductor drift generally from:

A. Positive to negative

B. Negative to positive

C. Both terminals to centre

D. No direction

Answer: B

Q11. Resistance of a wire is directly proportional to:

A. Cross-sectional area

B. Length

C. Conductivity only

D. Current only

Answer: B

Q12. Resistance is inversely proportional to:

A. Length

B. Resistivity

C. Area of cross-section

D. Time

Answer: C

Q13. Resistivity is a property of:

A. Material

B. Length only

C. Area only

D. Circuit shape only

Answer: A

Q14. Equivalent resistance in series is:

A. R₁R₂

B. R₁ + R₂ + R₃

C. R₁/R₂

D. Always zero

Answer: B

Q15. In a parallel circuit, the potential difference across each branch is:

A. Same

B. Zero

C. Always different

D. Infinite

Answer: A

Q16. In series connection, current through each resistor is:

A. Different

B. Same

C. Zero

D. Infinite

Answer: B

Q17. Equivalent resistance of parallel combination is:

A. Greater than every resistor

B. Equal to largest resistor

C. Less than the smallest resistor

D. Always zero

Answer: C

Q18. One volt is equal to:

A. 1 J/C

B. 1 C/J

C. 1 A/C

D. 1 Ω/C

Answer: A

Q19. One ohm is:

A. 1 A/V

B. 1 V/A

C. 1 C/V

D. 1 J/A

Answer: B

Q20. Which instrument measures current?

A. Voltmeter

B. Galvanometer only

C. Ammeter

D. Barometer

Answer: C

Q21. Which instrument measures potential difference?

A. Voltmeter

B. Ammeter

C. Thermometer

D. Speedometer

Answer: A

Q22. A closed circuit has:

A. Complete conducting path

B. Broken path

C. No source

D. No conductor

Answer: A

Q23. A 10 C charge flows in 2 s. Current is:

A. 2 A

B. 5 A

C. 10 A

D. 20 A

Answer: B

Q24. If V = 20 V and R = 5 Ω, current is:

A. 2 A

B. 3 A

C. 4 A

D. 5 A

Answer: C

Q25. If I = 2 A and R = 6 Ω, V is:

A. 12 V

B. 3 V

C. 8 V

D. 4 V

Answer: A

Q26. If the length of a wire is doubled, keeping area and material constant, resistance becomes:

A. Half

B. Double

C. Four times

D. One-fourth

Answer: B

Q27. If cross-sectional area is doubled, resistance becomes:

A. Double

B. Four times

C. Half

D. Same

Answer: C

Q28. Household appliances are generally connected in:

A. Series

B. Parallel

C. Only one branch

D. No circuit

Answer: B

Q29. The SI unit of resistivity is:

A. Ω m

B. Ω/m

C. V/m

D. A/m

Answer: A

Q30. Which relation is correct?

A. R = ρA/L

B. R = ρL/A

C. R = ρLA

D. R = L/ρA

Answer: B

24. 30 Subjective Questions with Answers

2 Marks Q1. Define electric current.

Electric current is the rate of flow of electric charge through a conductor.
I = Q/t

2 Marks Q2. Write the SI unit of electric current.

The SI unit is ampere (A).

2 Marks Q3. What is an electric circuit?

A continuous conducting path through which electric current can flow is called an electric circuit.

2 Marks Q4. What is potential difference?

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

2 Marks Q5. State the SI unit of resistance.

The SI unit of resistance is ohm (Ω).

3 Marks Q6. Differentiate between open and closed circuit.

Open circuit → path incomplete, current does not flow.
Closed circuit → path complete, current flows.

3 Marks Q7. Why is an ammeter connected in series?

An ammeter measures the current flowing through a component, so the same current must pass through the ammeter. Therefore it is connected in series.

3 Marks Q8. Why is a voltmeter connected in parallel?

A voltmeter measures potential difference between two points. Therefore it is connected across the component in parallel.

3 Marks Q9. State Ohm's law.

At constant temperature, potential difference across a conductor is directly proportional to current through it. Hence V = IR.

3 Marks Q10. What is resistance?

Resistance is the property of a conductor that opposes the flow of electric current. R = V/I.

4 Marks Q11. Explain the factors affecting resistance.

Resistance depends on:

• Length: R ∝ L
• Area: R ∝ 1/A
• Material: through resistivity ρ
• Temperature

4 Marks Q12. Derive the relation R = ρL/A.

For a uniform conductor, resistance is directly proportional to length and inversely proportional to cross-sectional area:
R ∝ L/A
Introducing proportionality constant ρ:
R = ρL/A

4 Marks Q13. Write two differences between series and parallel connection.

Series: same current, single path.
Parallel: same potential difference across branches, multiple paths.

4 Marks Q14. Why are household appliances connected in parallel?

They receive the same supply voltage and can be operated independently. Failure of one appliance does not necessarily stop the others.

4 Marks Q15. Explain conventional current and electron flow.

Conventional current is taken from positive to negative terminal externally. Electrons in metallic conductors drift in the opposite direction, from negative to positive.

5 Marks Q16. Explain electric current with formula and unit.

Electric current is charge flowing per unit time:
I = Q/t
SI unit is ampere.
1 A = 1 C/s.

5 Marks Q17. Explain series combination of resistors.

In series:
R = R₁ + R₂ + R₃
Current is same through all resistors and potential difference is divided.

5 Marks Q18. Explain parallel combination of resistors.

In parallel:
1/R = 1/R₁ + 1/R₂ + 1/R₃
Potential difference is the same across each branch and current divides among branches.

5 Marks Q19. Explain the importance of a cell in an electric circuit.

A cell provides potential difference by converting chemical energy into electrical energy. This potential difference drives charge through the external circuit.

5 Marks Q20. Explain resistivity.

Resistivity is a material property describing opposition to current flow:
ρ = RA/L
SI unit is Ω m.

6 Marks Q21. Explain a simple electric circuit with a labelled diagram.

A simple circuit consists of a cell/battery, wires, switch and load such as a bulb. When the switch is closed, the conducting path becomes complete and current flows through the bulb.

6 Marks Q22. Explain Ohm's law and its V-I graph.

At constant temperature:
V ∝ I
Therefore V = IR.
For an ohmic conductor, the V-I graph is a straight line passing through the origin and its slope represents resistance.

6 Marks Q23. Compare series and parallel combinations.

Series	Parallel
Single path	Multiple paths
Same current	Same potential difference
R = R₁+R₂+...	1/R = 1/R₁+1/R₂+...
Equivalent R is larger	Equivalent R is smaller than smallest branch R

6 Marks Q24. Solve: A 24 V source is connected to a 6 Ω resistor. Find current.

I = V/R
I = 24/6
I = 4 A

6 Marks Q25. Two resistors 5 Ω and 10 Ω are connected in series across 30 V. Find current.

R = 5+10 = 15 Ω
I = 30/15
I = 2 A

6 Marks Q26. Two resistors 6 Ω and 12 Ω are connected in parallel. Find equivalent resistance.

1/R = 1/6 + 1/12
1/R = 2/12 + 1/12
1/R = 3/12 = 1/4
R = 4 Ω

6 Marks Q27. Explain why increasing the length of a wire increases its resistance.

A longer conductor provides a greater distance over which charge carriers encounter the material's resistance. Therefore R ∝ L.

6 Marks Q28. Explain why a thick wire has less resistance than a thin wire of the same material and length.

A thick wire has greater cross-sectional area. Since R ∝ 1/A, increasing area decreases resistance.

6 Marks Q29. Explain the difference between resistance and resistivity.

Resistance depends on length, area, material and temperature of a particular conductor. Resistivity is a characteristic property of the material at a given temperature.

6 Marks Q30. Explain all important equations of the topic.

• I = Q/t
• V = W/Q
• V = IR
• R = ρL/A
• R_series = R₁+R₂+R₃
• 1/R_parallel = 1/R₁+1/R₂+1/R₃

25. Assertion–Reason

Q1. Assertion: Ammeter is connected in series.
Reason: The same current must pass through the ammeter and the component.

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

Q2. Assertion: Voltmeter is connected in parallel.
Reason: It measures potential difference between two points.

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

Q3. Assertion: Increasing the length of a wire increases its resistance.
Reason: R ∝ L for a uniform conductor at fixed material and temperature.

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

Q4. Assertion: Equivalent resistance of parallel resistors is less than the smallest resistor.
Reason: Parallel connection provides multiple paths for current.

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

Q5. Assertion: Current is same through every branch of a parallel circuit.
Reason: Potential difference is same across parallel branches.

Answer: Assertion is false; Reason is true.

26. HOTS | Higher Order Thinking

HOTS 1. Why does a thick copper wire have less resistance than a thin copper wire of the same length?

The thick wire has greater cross-sectional area. Since R = ρL/A, greater A gives lower R.

HOTS 2. Why does adding another resistor in series increase total resistance?

The equivalent resistance in series is the sum of individual resistances.

HOTS 3. Why does adding a parallel path reduce equivalent resistance?

Current gets additional paths to flow, increasing the total conductance and reducing equivalent resistance.

HOTS 4. What happens to current if voltage is doubled while resistance remains constant?

From I = V/R, current doubles.

HOTS 5. Why should a voltmeter have high resistance?

High resistance ensures that it draws very little current from the circuit and minimally disturbs the circuit being measured.

27. Diagram Labelling Practice

Identify the following components in an electric circuit:

1. Cell/Battery
2. Connecting wire
3. Switch
4. Bulb/Load
5. Ammeter
6. Voltmeter

Key: Ammeter → Series; Voltmeter → Parallel; Cell → Source of potential difference; Switch → Opens/closes circuit.

28. CBSE Golden Points ⭐

1. Electric current is rate of flow of charge.
2. I = Q/t.
3. SI unit of current is ampere.
4. Conventional current flows from positive to negative externally.
5. Electrons drift in the opposite direction in metallic conductors.
6. Ammeter is connected in series.
7. Voltmeter is connected in parallel.
8. Ohm's law: V = IR.
9. Resistance opposes current.
10. R = ρL/A.
11. Series resistance is the sum of resistances.
12. Parallel equivalent resistance is less than the smallest branch resistance.
13. Household appliances are connected in parallel.
14. Resistivity is a material property.
15. Potential difference is measured in volts.

29. Memory Tricks 🧠

⚡ Trick 1: Current

Current = Charge / Time
I = Q/t

⚡ Trick 2: Ohm's Law

V = IR
Voltage = Current × Resistance

⚡ Trick 3: Meter Connection

Ammeter → Always in Series
Voltmeter → Across the component

⚡ Trick 4: Resistance

Longer wire → More resistance
Thicker wire → Less resistance

⚡ Trick 5: Series

Series = Same Current

⚡ Trick 6: Parallel

Parallel = Same Voltage

30. One-Minute Revision ⚡

🔋 Cell provides potential difference.

⚡ Charge flows through a closed conducting path.

📏 Current = Q/t.

🔌 Potential difference = W/Q.

📐 Ohm's law = V = IR.

🧱 Resistance = opposition to current.

📏 R = ρL/A.

➕ Series → same current.

↔️ Parallel → same voltage.

📟 Ammeter → series.

📟 Voltmeter → parallel.

31. Concept Map

🔋 Cell / Battery
↓ ⚡ Potential Difference
↓ 🔌 Closed Electric Circuit
↓ ⚡ Electric Current
↓ 🧱 Resistance
↓ 📐 Ohm's Law
V = IR
↓ 🔗 Series / Parallel Combination
↓ 💡 Electrical Appliances

32. Final Summary | अंतिम सारांश

Electric current is the rate of flow of electric charge through a conductor. The basic relation is:

I = Q/t

Potential difference provides the electrical driving force:

V = W/Q

For an ohmic conductor at constant temperature:

V = IR

Resistance of a uniform conductor is:

R = ρL/A

In series, resistances add directly. In parallel, reciprocal resistances add. Ammeter is connected in series, whereas voltmeter is connected in parallel.

⚡ Charge → Current → Resistance → Potential Difference → Circuit

⚡ Electricity

Electric Current and Electric Circuit

विद्युत धारा एवं विद्युत परिपथ

Class 10 Science | CBSE + Foundation + Competitive