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Current Electricity MCQs — Physics (page 5)

270 multiple-choice questions on Current Electricity from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

101. A potentiometer can compare two resistances R1 and R2 carrying the same current by comparing:

  1. their masses
  2. their temperatures
  3. the balance lengths for the p.d.s across them
  4. their colours

Answer: C) the balance lengths for the p.d.s across them

Explanation: R1R2 = l1l2. SLO P-09-E-23 · Application

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102. Household appliances are connected in parallel so that:

  1. they share the voltage
  2. they all switch together
  3. each gets the full mains voltage and can be switched independently
  4. the current is the same in each

Answer: C) each gets the full mains voltage and can be switched independently

Explanation: Parallel wiring. SLO P-09-E-21 · Application

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103. An NTC thermistor and fixed resistor form a potential divider; output across the fixed resistor. As temperature rises, the output:

  1. stays the same
  2. decreases
  3. increases
  4. reverses

Answer: C) increases

Explanation: Thermistor resistance falls, so the fixed resistor's share rises. SLO P-09-E-25 · Understanding

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104. Kirchhoff's first law is also called:

  1. the loop rule
  2. the junction rule (current law)
  3. Lenz's law
  4. Ohm's law

Answer: B) the junction rule (current law)

Explanation: KCL. SLO P-09-E-18 · Knowledge

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105. A 6 Ω resistor is connected to 12 V. The power is:

  1. 24 W
  2. 48 W
  3. 2 W
  4. 72 W

Answer: A) 24 W

Explanation: P = V^2R = 12^26 = 24 W. SLO P-09-E-12 · Application

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106. Connecting more lamps in parallel to a battery with internal resistance makes each lamp:

  1. slightly dimmer
  2. go out
  3. unchanged
  4. brighter

Answer: A) slightly dimmer

Explanation: Larger current ⇒ more lost volts ⇒ lower terminal p.d. SLO P-09-E-26 · Understanding

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107. Both e.m.f. and p.d. are measured in:

  1. amperes
  2. volts
  3. ohms
  4. joules

Answer: B) volts

Explanation: Energy per unit charge. SLO P-09-E-16 · Understanding

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108. If the current in a wire is doubled, the drift velocity:

  1. halves
  2. quadruples
  3. stays the same
  4. doubles

Answer: D) doubles

Explanation: v propto I. SLO P-09-E-10 · Application

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109. The resistance of an NTC thermistor:

  1. decreases as temperature increases
  2. depends on light
  3. increases as temperature increases
  4. is constant

Answer: A) decreases as temperature increases

Explanation: Negative temperature coefficient. SLO P-09-E-25 · Understanding

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110. A null method compares two quantities by:

  1. adding them
  2. adjusting until their effects cancel
  3. measuring each separately with a meter
  4. multiplying them

Answer: B) adjusting until their effects cancel

Explanation: Balance. SLO P-09-E-24 · Understanding

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111. A wire is stretched to twice its length (same volume). Its resistance becomes:

  1. half
  2. unchanged
  3. 2 times as large
  4. 4 times as large

Answer: D) 4 times as large

Explanation: Length doubles, area halves. SLO P-09-E-13 · Application

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112. A 6 Ω and a 3 Ω resistor in parallel across 6 V: the total current is:

  1. 1 A
  2. 2 A
  3. 3 A
  4. 0.67 A

Answer: C) 3 A

Explanation: 1 + 2 = 3 A. SLO P-09-E-21 · Application

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113. Resistors of 2 Ω, 4 Ω are in series with a 12 V supply. The current is:

  1. 6 A
  2. 2 A
  3. 4 A
  4. 1 A

Answer: B) 2 A

Explanation: R = 6 Ω; I = VR = 2 A. SLO P-09-E-20 · Application

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114. A fire alarm should switch on when hot. Using an NTC thermistor, the output should be taken across:

  1. the fixed resistor
  2. the thermistor
  3. an ammeter
  4. the supply

Answer: A) the fixed resistor

Explanation: Output rises with temperature. SLO P-09-E-25 · Understanding

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115. Which statement is correct?

  1. p.d. is associated with sources only
  2. e.m.f. is measured in amperes
  3. e.m.f. and p.d. are always equal
  4. e.m.f. is associated with sources; p.d. with components that use energy

Answer: D) e.m.f. is associated with sources; p.d. with components that use energy

Explanation: Energy in vs energy out. SLO P-09-E-16 · Understanding

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116. A potentiometer is better than a voltmeter for measuring e.m.f. because a voltmeter:

  1. has infinite resistance
  2. is more accurate always
  3. measures current
  4. draws some current, so it reads the terminal p.d.

Answer: D) draws some current, so it reads the terminal p.d.

Explanation: Potentiometer is a null method. SLO P-09-E-23 · Application

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117. The combined resistance of resistors in parallel is:

  1. equal to the sum
  2. equal to the largest
  3. less than the smallest individual resistance
  4. more than the largest

Answer: C) less than the smallest individual resistance

Explanation: More paths for current. SLO P-09-E-21 · Application

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118. Two wires A and B of the same material: A is twice as long and has twice the diameter of B. The ratio RA : RB is:

  1. 2 : 1
  2. 4 : 1
  3. 1 : 1
  4. 1 : 2

Answer: D) 1 : 2

Explanation: R propto Ld^2: 24 = 12. SLO P-09-E-13 · Application

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119. How many independent equations from Kirchhoff's first law are needed for a circuit with 3 junctions?

  1. 3
  2. 4
  3. 2
  4. 1

Answer: C) 2

Explanation: One fewer than the number of junctions. SLO P-09-E-22 · Application

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120. A lamp has a p.d. of 3 V across it. Each coulomb passing through it:

  1. loses 3 C
  2. transfers 3 J to heat and light
  3. gains 3 J
  4. gains 3 A

Answer: B) transfers 3 J to heat and light

Explanation: Energy out. SLO P-09-E-16 · Understanding

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121. Light reduces the resistance of an LDR because it:

  1. heats the wire
  2. makes it magnetic
  3. makes it longer
  4. frees more electrons to conduct

Answer: D) frees more electrons to conduct

Explanation: Photoconductivity. SLO P-09-E-14 · Knowledge

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122. A 9 V battery gives each coulomb passing through it:

  1. 9 A of current
  2. 9 N of force
  3. 9 J of energy
  4. 9 C of charge

Answer: C) 9 J of energy

Explanation: e.m.f. = energy per coulomb. SLO P-09-E-15 · Application

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123. Resistors of 10 Ω, 20 Ω are connected in series. The combined resistance is:

  1. 300 Ω
  2. 15 Ω
  3. 60 Ω
  4. 30 Ω

Answer: D) 30 Ω

Explanation: R = R1 + R2 + ldots = 30 Ω. SLO P-09-E-20 · Application

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124. If the light on an LDR in series with a fixed resistor increases, the current in the circuit:

  1. increases
  2. decreases
  3. becomes zero
  4. stays the same

Answer: A) increases

Explanation: Total resistance falls. SLO P-09-E-14 · Knowledge

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125. A solar cell's e.m.f. comes from converting:

  1. nuclear energy
  2. chemical energy
  3. kinetic energy
  4. light energy into electrical energy

Answer: D) light energy into electrical energy

Explanation: Photovoltaic effect. SLO P-09-E-15 · Application

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