10th Physics Current Electricity Solved Exercises - Federal Board Chapter 16 Notes

10th Physics Federal Board Notes: Chapter 16 Current Electricity

Complete solved exercises with MCQs, short questions, and long questions. Perfect preparation for 10th class physics exams.

10th Physics Federal Board Chapter 16 Notes Current Electricity Ohm's Law Solved Exercises Reading Time: 25 min

📋 Table of Contents

1. Multiple Choice Questions (MCQs)
2. Constructed Response Questions
- 2.1 EMF Sources Connection
- 2.2 Ammeters and Voltmeters
3. Short Answer Questions
4. Long Answer Questions

⚡ Introduction to Current Electricity

Chapter 16: Current Electricity explores the fundamental concepts of electric current, resistance, and electrical circuits. This chapter covers essential topics including Ohm's law, electrical measurements, circuit components, and practical applications. Understanding these concepts is crucial for comprehending how electrical devices work and for solving real-world electrical problems.

Multiple Choice Questions (MCQs)

1. Ampere-hour (Ah) is the unit of:

A. electric current

B. charge

C. energy

D. resistance

Correct Answer: B
Ampere-hour represents the amount of charge transferred when a current of one ampere flows for one hour. 1 Ah = 3600 Coulombs.

2. Which of the following is a non-ohmic device?

A. Copper wire

B. Carbon resistor

C. Diode

D. all of these

Correct Answer: C
A diode is non-ohmic because it doesn't follow Ohm's law - its resistance changes with voltage and current direction.

3. Electric current is measured using:

A. ammeter

B. voltmeter

C. ohmmeter

D. meter rod

Correct Answer: A
Ammeter is specifically designed to measure electric current and is always connected in series with the circuit.

4. Voltmeter measures:

A. potential difference

B. electric current

C. resistance

D. resistivity

Correct Answer: A
Voltmeter measures the potential difference between two points in a circuit and is always connected in parallel.

5. If 3 A of current flows for 2 minutes, the amount of charge crosses the cross-section of a conductor will be:

A. 3 C

B. 6 C

C. 60 C

D. 360 C

Correct Answer: D
Using Q = I × t = 3 A × 120 s = 360 C. Remember to convert minutes to seconds.

6. A current of 1 mA is passing through a wire. Number of electrons passing through a point in the wire in 10 seconds is:

A. \( 6.25 \times 10^{19} \)

B. \( 6.25 \times 10^{18} \)

C. \( 6.25 \times 10^{17} \)

D. \( 6.25 \times 10^{16} \)

Correct Answer: D
Charge Q = I × t = 0.001 A × 10 s = 0.01 C
Number of electrons = Q/e = 0.01 C / (1.6 × 10⁻¹⁹ C) = 6.25 × 10¹⁶ electrons

7. Resistance of a material always decreases when:

A. its temperature increases

B. its temperature decreases

C. Number of free electrons increases

D. Number of free electrons decreases

Correct Answer: C
More free electrons mean better conductivity and lower resistance, as there are more charge carriers available.

8. The resistance of a metallic conductor varies inversely as:

A. area of cross section

B. length

C. temperature

D. all of these

Correct Answer: A
According to R = ρL/A, resistance is inversely proportional to cross-sectional area and directly proportional to length.

9. Directions of actual current and conventional current are:

A. same

B. opposite to each other

C. perpendicular to each other

D. none of these

Correct Answer: B
Conventional current flows from positive to negative, while actual electron flow is from negative to positive.

10. As temperature of a semiconductor increases, its resistance:

A. increases

B. decreases

C. remains constant

D. becomes zero

Correct Answer: B
In semiconductors, higher temperature creates more charge carriers, decreasing resistance - opposite to metals.

11. The SI unit of temperature coefficient of resistance (α) is:

A. K

B. K⁻¹

C. ΩK

D. Ω/K

Correct Answer: B
Temperature coefficient has units of per degree (K⁻¹ or °C⁻¹) as it represents resistance change per degree temperature change.

12. By increasing temperature, the resistivity of semiconductors:

A. increases

B. decreases

C. remains constant

D. first increases then decreases

Correct Answer: B
Semiconductor resistivity decreases with temperature due to increased charge carrier concentration.

Constructed Response Questions

Q1. Draw connections so that the emf sources given in figure become in series and parallel.

🔌 EMF Sources Connection Methods

Series Connection:

Connect positive terminal of ε₁ to negative terminal of ε₂
Connect positive terminal of ε₂ to negative terminal of ε₃
Connect positive terminal of ε₃ to negative terminal of ε₄
Total EMF = ε₁ + ε₂ + ε₃ + ε₄
Current capacity remains same as single source

Parallel Connection:

Connect all positive terminals together
Connect all negative terminals together
Total EMF = EMF of single source (if identical)
Current capacity increases (sum of individual capacities)

Q2. Compare and contrast the roles of ammeters and voltmeters in electrical circuits.

Aspect	Ammeter	Voltmeter
Function	Measures electric current	Measures potential difference
Connection	Series connection	Parallel connection
Internal Resistance	Very low (to minimize voltage drop)	Very high (to minimize current draw)
Units	Amperes (A)	Volts (V)
Impact on Circuit	Becomes part of current path	Measures across components without interrupting current

Short Answer Questions

Q1. Why is copper preferred over silver for household wiring, considering cost, conductivity, and durability?

🏠 Copper vs Silver for Household Wiring

Cost Factor: Silver is significantly more expensive than copper, making copper economically practical for large-scale wiring projects.

Conductivity: While silver has slightly better conductivity (6.30×10⁷ S/m vs copper's 5.96×10⁷ S/m), the difference is minimal for household applications.

Durability: Copper offers excellent corrosion resistance and mechanical strength, making it reliable for long-term use.

Practical Considerations: Copper is more abundant, easier to work with, and meets all electrical safety standards.

Q2. Why free electrons in metals don't create a current without a potential difference?

🔬 Free Electrons and Current Flow

Free electrons in metals move randomly due to thermal energy, but this motion is:

Random in direction - electrons move in all directions equally
No net flow - equal numbers move in opposite directions
Zero average velocity - no preferred direction of motion

A potential difference creates an electric field that exerts a net force on electrons, causing them to drift in a specific direction, creating current.

Q3. How conventional and actual current directions affect circuit behaviour, and why conventional current is important in diagrams and calculations?

Aspect	Conventional Current	Actual Current (Electron Flow)
Direction	Positive to negative	Negative to positive
Historical Basis	Established before electron discovery	Based on actual particle movement
Usage	Standard in circuit diagrams and analysis	Used in semiconductor physics
Circuit Behavior	Same mathematical results	Same mathematical results

Q4. Compare e.m.f and potential difference, and why this distinction matters in circuit analysis.

Parameter	Electromotive Force (EMF)	Potential Difference (PD)
Definition	Energy supplied by source per unit charge	Energy used by charge between two points
Symbol	ε or E	V
Measurement	Across source terminals (no current)	Between any two circuit points
Cause	Source characteristics	Circuit resistance and current
Value	Constant for ideal source	Depends on circuit conditions

Q5. How is a current-carrying wire electrically neutral?

⚖️ Electrical Neutrality in Current Flow

A current-carrying wire remains electrically neutral because:

Equal positive and negative charges: Number of protons equals number of electrons
Continuous charge flow: Electrons entering wire equal electrons leaving wire
No net charge accumulation: Charge conservation maintains neutrality
Atomic structure unchanged: Current flow doesn't alter atomic composition

Think of it like water flowing through a pipe - the pipe itself doesn't gain or lose material.

Q6. Would the lights still work if a car battery's positive and negative terminals were interchanged?

⚠️ Car Battery Polarity Warning

No, the lights will NOT work and serious damage can occur:

Short circuit creation due to reversed polarity
Electronic component damage to ECU, sensors, and control units
Fuse blowing as protection mechanism
Potential fire hazard from overheating wires
Battery damage and reduced lifespan

Always connect car batteries with correct polarity to ensure safety and proper function.

Q7. Evaluate the limits of Ohm's law for different materials, especially under extreme conditions.

📊 Ohm's Law Limitations

Ohm's Law (V = IR) applies only to:

Ohmic materials (most metals at constant temperature)
Constant physical conditions

Limitations include:

Non-ohmic devices: Diodes, transistors, semiconductors
Temperature dependence: Resistance changes with temperature
Frequency effects: AC circuit behavior differs from DC
Extreme conditions: High voltages/currents, very low temperatures
Non-linear materials: Where I-V graph is not straight

Q8. How does a wire's shape affect its resistance, whether bending changes it?

📏 Wire Bending and Resistance

Bending generally does NOT change resistance because:

Length remains constant (unless stretching occurs)
Cross-sectional area unchanged (minor deformations negligible)
Resistivity unaffected (material property unchanged)

Resistance depends on:

Material resistivity (ρ)
Length (L)
Cross-sectional area (A)
Formula: R = ρL/A

Only if bending causes permanent deformation or damage will resistance change significantly.

Q9. The temperature coefficient of copper is 0.004 °C⁻¹. How does this affect copper's performance in electrical systems under varying temperatures?

🌡️ Temperature Effects on Copper

With α = 0.004 °C⁻¹, copper's resistance increases with temperature:

At Higher Temperatures:

Resistance increases: R = R₀[1 + α(T - T₀)]
Current decreases for constant voltage: I = V/R
Power dissipation increases: P = I²R
Voltage drops become larger

At Lower Temperatures:

Resistance decreases
Current increases for constant voltage
Power dissipation decreases
Improved efficiency

Design Considerations: Account for temperature variations in electrical system design.

Q10. How would you define fluid resistance for a water-carrying pipe?

💧 Fluid Resistance Analogy

Fluid resistance in pipes opposes water flow, similar to electrical resistance opposing current flow.

Causes of Fluid Resistance:

Viscosity: Internal fluid friction
Wall friction: Roughness of pipe interior
Turbulence: Chaotic flow patterns
Fittings/obstructions: Valves, bends, restrictions

Analogous to Electrical Concepts:

Pressure difference ↔ Potential difference
Flow rate ↔ Current
Pipe resistance ↔ Electrical resistance
Pump ↔ Battery/EMF source

Long Answer Questions

Q1. Explain electric current and its unit (ampere) by exploring charge flow. Discuss the difference between conventional and actual current and when this distinction matters.

⚡ Electric Current Fundamentals

Electric Current Definition:

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

\[ I = \frac{Q}{t} \] Where:
I = Electric current (Amperes)
Q = Charge (Coulombs)
t = Time (seconds)

Ampere Definition:

One ampere is defined as one coulomb of charge flowing per second.

\[ 1 A = 1 \frac{C}{s} \]

Conventional vs Actual Current:

Conventional Current: Direction of positive charge flow (positive to negative)
Actual Current: Direction of electron flow (negative to positive)
Importance: Distinction matters in semiconductor devices, Hall effect, and electrochemistry

Q2. Analyze electrical conduction in metals and how external factors like temperature and magnetic fields affect electron movement and conduction efficiency.

🔬 Electrical Conduction in Metals

Conduction Mechanism:

Metals have "sea" of free electrons
Electrons move randomly at high speeds
Applied electric field causes net drift velocity
Current proportional to drift velocity

Temperature Effects:

Increased temperature → increased atomic vibrations
More electron scattering → higher resistance
Reduced conductivity and efficiency

Magnetic Field Effects:

Lorentz force deflects moving electrons
Hall effect creates voltage perpendicular to current
Can reduce effective conductivity

Q3. Compare DC and AC in terms of their behaviour in circuit elements. Discuss the pros and cons of each in applications like power transmission and electronics.

Aspect	Direct Current (DC)	Alternating Current (AC)
Definition	Unidirectional flow	Periodically reversing flow
Resistors	Constant current for constant voltage	Alternating current for AC voltage
Capacitors	Blocks DC after charging	Allows AC (frequency dependent)
Inductors	Short circuit for DC	Opposes AC (frequency dependent)
Power Transmission	Higher losses over distance	Efficient long-distance transmission
Electronics	Preferred for digital circuits	Requires rectification for electronics

Q4. Examine electromotive force (emf) and its role in maintaining current.

🔋 Electromotive Force (EMF)

Definition: EMF is the energy supplied by a source per unit charge to drive current through a circuit.

Role in Maintaining Current:

Creates potential difference between terminals
Provides energy to move charges against resistance
Overcomes internal resistance of source
Sustains continuous current flow in closed circuit

Analogy: EMF acts like a water pump that maintains water flow against pipe resistance.

Mathematical Representation:

\[ \varepsilon = I(R + r) \] Where:
ε = EMF
I = Current
R = External resistance
r = Internal resistance

Q5. Distinguish between emf and potential difference, using real-world examples like batteries.

🔌 EMF vs Potential Difference in Batteries

EMF (ε):

Maximum voltage battery can provide
Measured when no current flows (open circuit)
Represents total energy per charge available
Example: 1.5V printed on AA battery label

Potential Difference (V):

Actual voltage across terminals during use
Always less than EMF due to internal resistance
Depends on current drawn from battery
Example: 1.4V measured when battery powers a circuit

Numerical Example:

For 1.5V battery with 0.1Ω internal resistance delivering 1A:
= ε - Ir
= 1.5V - (1A × 0.1Ω)
= 1.4V terminal voltage

Q6. Critically analyse Ohm's law and its limitations for non-ohmic devices. Discuss the importance of I-V graphs and propose experiments to explore non-linear materials.

📈 Ohm's Law Analysis and I-V Graphs

Ohm's Law Statement: V = IR (for constant temperature)

Limitations:

Non-ohmic devices don't follow linear relationship
Temperature changes affect resistance
Frequency-dependent behavior in AC circuits
Breakdown at extreme voltages/currents

I-V Graph Importance:

Visual representation of device behavior
Slope gives resistance at any point
Identifies ohmic vs non-ohmic characteristics
Essential for circuit design and analysis

Experiments for Non-linear Materials:

Diode Characteristics: Measure I-V curve showing forward and reverse bias regions
Thermistor Study: Measure resistance changes with temperature
Filament Lamp: Observe resistance increase with temperature

Q7. Investigate the relationship between resistance and resistivity and design an experiment to measure resistance. Discuss factors affecting accuracy, such as temperature.

🔍 Resistance and Resistivity Relationship

Fundamental Relationship:

\[ R = \rho \frac{L}{A} \] Where:
R = Resistance (Ω)
ρ = Resistivity (Ω·m)
L = Length (m)
A = Cross-sectional area (m²)

Experiment to Measure Resistance:

Measure Dimensions: Length with ruler, diameter with micrometer
Calculate Area: A = π(d/2)² for circular wire
Circuit Setup: Wire in series with ammeter, voltmeter in parallel
Data Collection: Multiple V-I readings at different voltages
Calculate R: R = V/I for each reading, then average
Determine ρ: ρ = RA/L using average R

Accuracy Factors:

Temperature: Use low currents to minimize heating
Contact Resistance: Ensure clean, tight connections
Meter Accuracy: Use calibrated instruments
Wire Uniformity: Check diameter consistency

Q8. Analyze how factors like temperature, material, length, and area affect resistance. Discuss practical applications, such as wiring or heating elements, and ways to optimize resistance.

📊 Factors Affecting Resistance

Resistance Formula: R = ρL/A

Factor Analysis:

Material (ρ): Different materials have different inherent resistivities
Length (L): Directly proportional - longer means higher resistance
Area (A): Inversely proportional - thicker means lower resistance
Temperature: Affects ρ - increases for metals, decreases for semiconductors

Practical Applications:

Wiring: Use low ρ materials (copper) with large A to minimize resistance
Heating Elements: Use high ρ materials (nichrome) with controlled L and A
Resistors: Precise control of all factors for specific resistance values

Optimization Strategies:

Material selection based on application requirements
Geometric design for desired resistance
Temperature management for stable operation
Quality control in manufacturing

Q9. How does temperature influence the resistance of materials, and what implications does this have for electrical components in different environments?

🌡️ Temperature-Resistance Relationship

Temperature Dependence: R = R₀[1 + α(T - T₀)]

Material Behavior:

Metals: Positive α - resistance increases with temperature
Semiconductors: Negative α - resistance decreases with temperature
Superconductors: Zero resistance below critical temperature

Component Implications:

Power Devices: Heating increases resistance, reducing efficiency
Sensors: Thermistors use temperature-resistance relationship
Circuit Design: Must account for operating temperature range
Reliability: Thermal stress affects component lifespan

Environmental Considerations:

Outdoor equipment must withstand temperature variations
Electronic devices need thermal management systems
Calibration must consider operating temperature

Q10. Examine the placement of ammeters and voltmeters in circuits and how misconnection affects measurement. Propose strategies to avoid errors.

📏 Ammeter and Voltmeter Placement

Correct Placement:

Ammeter: Series connection to measure current through component
Voltmeter: Parallel connection to measure voltage across component

Misconnection Consequences:

Ammeter in Parallel: Short circuit risk, meter damage, incorrect readings
Voltmeter in Series: High resistance reduces current, incorrect voltage measurement

Error Prevention Strategies:

Understand instrument function before connection
Follow circuit diagrams precisely
Verify polarity for DC measurements
Use appropriate measurement ranges
Check instrument settings before use
Practice with simple circuits first

Safety Considerations:

Start with lowest measurement ranges
Disconnect power before making connections
Use proper personal protective equipment
Follow laboratory safety protocols

📚 Master 10th Physics Current Electricity

This comprehensive guide covers all essential concepts from Chapter 16 Current Electricity. Understanding electric current, resistance, circuits, and electrical measurements is crucial for both academic success and practical electrical knowledge.

Key Topics Covered: Ohm's law, circuit analysis, electrical measurements, EMF vs potential difference, resistance calculations, and practical applications.

Complete solved exercises based on Federal Board curriculum with detailed explanations and practical applications

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