Chapter 13 Quiz: Electric Circuits

Instructions

This quiz tests your understanding of electric circuits, including current, resistance, Ohm's Law, capacitors, inductors, power sources, and applications like solar power systems and electric motors. Select the best answer for each question.

Question 1: Electric Current

Concept: Electric Current | Bloom's Level: Remembering

What is the SI unit of electric current?

A) Volt (V)
B) Ohm (Ω)
C) Ampere (A)
D) Watt (W)

Answer

C) Ampere (A)

Electric current is measured in amperes (A), where 1 ampere equals 1 coulomb of charge flowing past a point per second (1 A = 1 C/s).

Question 2: Current Direction

Concept: Conventional Current vs Electron Flow | Bloom's Level: Understanding

In a simple circuit with a battery and resistor, conventional current flows:

A) From negative terminal through the circuit to positive terminal
B) From positive terminal through the circuit to negative terminal
C) In both directions simultaneously
D) Only when the circuit is open

Answer

B) From positive terminal through the circuit to negative terminal

Conventional current is defined as the direction positive charges would flow—from positive to negative terminal. This is opposite to the actual electron flow (negative to positive), but both conventions give the same results for circuit analysis.

Question 3: Ohm's Law Calculation

Concept: Ohm's Law | Bloom's Level: Applying

A 6V battery is connected to a resistor, and 0.02 A of current flows. What is the resistance?

A) 0.12 Ω
B) 3 Ω
C) 120 Ω
D) 300 Ω

Answer

D) 300 Ω

Using Ohm's Law: R = V/I = 6 V / 0.02 A = 300 Ω

Question 4: Resistance Factors

Concept: Resistance | Bloom's Level: Understanding

Which change would DECREASE the resistance of a copper wire?

A) Making the wire longer
B) Making the wire thinner
C) Increasing the temperature
D) Making the wire thicker

Answer

D) Making the wire thicker

Resistance is inversely proportional to cross-sectional area (R ∝ 1/A). A thicker wire has more area for electrons to flow through, reducing resistance. Longer wires, thinner wires, and higher temperatures all increase resistance.

Question 5: Power Calculation

Concept: Electric Power | Bloom's Level: Applying

A device operates at 12V and draws 2A of current. How much power does it consume?

A) 6 W
B) 14 W
C) 24 W
D) 144 W

Answer

C) 24 W

Power = V × I = 12 V × 2 A = 24 W

Question 6: Series Circuit

Concept: Series Circuits | Bloom's Level: Applying

Three 100 Ω resistors are connected in series to a 9V battery. What is the current through each resistor?

A) 0.01 A
B) 0.03 A
C) 0.09 A
D) 0.30 A

Answer

B) 0.03 A

In a series circuit, total resistance = 100 + 100 + 100 = 300 Ω. Current = V/R = 9V / 300Ω = 0.03 A. In series, the same current flows through all components.

Question 7: Parallel Circuit

Concept: Parallel Circuits | Bloom's Level: Analyzing

Two resistors of 100 Ω and 200 Ω are connected in parallel. What is their equivalent resistance?

A) 50 Ω
B) 66.7 Ω
C) 150 Ω
D) 300 Ω

Answer

B) 66.7 Ω

For parallel resistors: 1/R_total = 1/R₁ + 1/R₂ = 1/100 + 1/200 = 3/200

R_total = 200/3 = 66.7 Ω

The equivalent resistance of parallel resistors is always less than the smallest individual resistor.

Question 8: Capacitor Energy Storage

Concept: Capacitance | Bloom's Level: Applying

A 100 μF capacitor is charged to 10V. How much energy is stored?

A) 0.005 J
B) 0.01 J
C) 0.5 J
D) 1.0 J

Answer

A) 0.005 J

Energy = ½CV² = ½ × (100 × 10⁻⁶ F) × (10 V)² = ½ × 0.0001 × 100 = 0.005 J = 5 mJ

Question 9: Capacitor Charging Behavior

Concept: RC Circuits | Bloom's Level: Understanding

When charging a capacitor through a resistor, the current:

A) Remains constant throughout charging
B) Starts at zero and increases exponentially
C) Starts at maximum and decreases exponentially
D) Oscillates between positive and negative values

Answer

C) Starts at maximum and decreases exponentially

When charging begins, the uncharged capacitor acts like a short circuit, allowing maximum current (I = V/R). As the capacitor charges, its voltage rises, opposing the battery voltage, so current decreases exponentially toward zero.

Question 10: Inductor Behavior

Concept: Inductance | Bloom's Level: Understanding

An inductor opposes changes in:

A) Voltage across it
B) Current through it
C) Temperature
D) Resistance

Answer

B) Current through it

Inductors oppose changes in current by generating a voltage (back-EMF) proportional to the rate of current change: V = L(dI/dt). This is electromagnetic inertia.

Question 11: DC vs AC

Concept: DC and AC Power Sources | Bloom's Level: Understanding

Which statement correctly describes AC power?

A) Current flows in only one direction
B) Voltage remains constant over time
C) Current periodically reverses direction
D) It cannot be used to power motors

Answer

C) Current periodically reverses direction

Alternating current (AC) periodically reverses direction, typically following a sinusoidal pattern. This is different from DC, where current flows continuously in one direction.

Question 12: Battery Capacity

Concept: Batteries | Bloom's Level: Applying

A 3.7V lithium-ion battery has a capacity of 2000 mAh. How much energy (in watt-hours) can it store?

A) 540 Wh
B) 7.4 Wh
C) 0.74 Wh
D) 74 Wh

Answer

B) 7.4 Wh

Energy = Voltage × Capacity = 3.7 V × 2 Ah = 7.4 Wh

(Note: 2000 mAh = 2 Ah)

Question 13: Solar Cell Operation

Concept: Solar Cells | Bloom's Level: Understanding

Solar cells convert light energy to electrical energy using:

A) The thermoelectric effect
B) The photovoltaic effect
C) Electromagnetic induction
D) Chemical reactions

Answer

B) The photovoltaic effect

Solar cells use the photovoltaic effect, where photons striking a semiconductor material (usually silicon) knock electrons loose, creating an electric current.

Question 14: Solar System Design

Concept: Solar Battery Systems | Bloom's Level: Analyzing

A solar lighting system uses 10W for 5 hours each night. With 4 peak sun hours available and 80% system efficiency, what minimum solar panel wattage is needed?

A) 10 W
B) 12.5 W
C) 15.6 W
D) 50 W

Answer

C) 15.6 W

Daily energy needed = 10 W × 5 h = 50 Wh

With 80% efficiency: 50 Wh / 0.8 = 62.5 Wh needed from panel

With 4 peak sun hours: 62.5 Wh / 4 h = 15.6 W minimum

Question 15: Motor Speed Control

Concept: Electric Motors | Bloom's Level: Understanding

In a DC motor, increasing the applied voltage will:

A) Decrease the motor speed
B) Increase the motor speed
C) Increase the resistance
D) Have no effect on speed

Answer

B) Increase the motor speed

DC motor speed is approximately proportional to applied voltage. Higher voltage creates a stronger magnetic force on the armature, causing it to spin faster. Speed ≈ (V - IR)/k, where k is the motor constant.

Question 16: Motor Back-EMF

Concept: Electric Motors | Bloom's Level: Analyzing

A DC motor runs at 1500 RPM with 12V applied, drawing 1A, and has an armature resistance of 2Ω. What is the back-EMF?

A) 2 V
B) 10 V
C) 12 V
D) 14 V

Answer

B) 10 V

Using V = IR + E_back:

12 V = (1 A)(2 Ω) + E_back

E_back = 12 - 2 = 10 V

The back-EMF opposes the applied voltage and is generated by the motor's rotation.

Question 17: Kirchhoff's Current Law

Concept: Kirchhoff's Laws | Bloom's Level: Applying

At a junction in a circuit, three wires carry currents of 2A, 3A, and 1A into the junction. A fourth wire carries current out. What current flows in the fourth wire?

A) 0 A
B) 2 A
C) 4 A
D) 6 A

Answer

D) 6 A

Kirchhoff's Current Law states that the sum of currents entering a junction equals the sum leaving. Current in = 2 + 3 + 1 = 6 A, so current out = 6 A.

Question 18: Energy Cost

Concept: Electric Power and Energy | Bloom's Level: Applying

An electric heater uses 1500 W. If electricity costs $0.12 per kWh, how much does it cost to run the heater for 8 hours?

A) $0.96
B) $1.44
C) $12.00
D) $14.40

Answer

B) $1.44

Energy = 1.5 kW × 8 h = 12 kWh

Cost = 12 kWh × $0.12/kWh = $1.44

Question 19: Time Constant

Concept: RC Circuits | Bloom's Level: Analyzing

An RC circuit has R = 10 kΩ and C = 100 μF. What is the time constant, and approximately how long does it take to fully charge the capacitor?

A) τ = 0.1 s, full charge ≈ 0.5 s
B) τ = 1 s, full charge ≈ 5 s
C) τ = 10 s, full charge ≈ 50 s
D) τ = 100 s, full charge ≈ 500 s

Answer

B) τ = 1 s, full charge ≈ 5 s

Time constant τ = RC = (10 × 10³ Ω)(100 × 10⁻⁶ F) = 1 s

A capacitor is considered fully charged after about 5 time constants (5τ), when it reaches 99.3% of final voltage.

Question 20: System Integration

Concept: Solar-Motor Systems | Bloom's Level: Evaluating

A solar-powered water pump system has a 50W panel, charges a 12V 20Ah battery, and runs a 15W pump. On a day with 5 hours of sun, approximately how many hours can the pump run after sunset?

A) 3 hours
B) 6 hours
C) 10 hours
D) 16 hours

Answer

D) 16 hours

Energy harvested: 50 W × 5 h = 250 Wh

Battery capacity: 12 V × 20 Ah = 240 Wh

Assuming the battery starts near full and can discharge to 50%: Available energy ≈ 240 Wh (fully charged during day)

Pump runtime = 240 Wh / 15 W = 16 hours

(In practice, accounting for inefficiencies, it would be somewhat less.)

Scoring Guide

Score	Performance Level
18-20	Excellent - Strong mastery of circuit concepts
15-17	Good - Solid understanding with minor gaps
12-14	Satisfactory - Core concepts understood, review recommended
9-11	Needs Improvement - Review chapter material
0-8	Unsatisfactory - Significant review needed

Concepts Covered

This quiz assessed understanding of:

Electric Current and Current Flow
Resistance and Ohm's Law
Electric Power
Series and Parallel Circuits
Capacitance and Capacitor Behavior
Inductance
DC and AC Power Sources
Batteries and Energy Storage
Solar Cells and Photovoltaics
Electric Motors and Speed Control
Kirchhoff's Laws
System Integration and Design