Current, Voltage & Resistance — Drills · Grade 12 Science

Chapter: Electricity, Magnetism & Circuits

What these drills covers

By the end of Current, Voltage & Resistance you should be able to:

6 questions, numeric, multiple choice and written answer, each with a worked explanation.

Vocabulary used: electric current, ampere (A), voltage (potential difference), resistance, resistivity.

Problem 1

A charge of 15 C flows past a point in 3 seconds. Find the current.
Answer and explanation

5 A

I = Q ÷ t = 15 ÷ 3 = 5 A.

Problem 2

Voltage is best described as:
  1. the resistance of the wire
  2. the speed of the electrons
  3. the energy given to each unit of charge
  4. the number of electrons in a wire
Answer and explanation

the energy given to each unit of charge

Voltage (potential difference) is the energy delivered per unit charge, V = W/Q, measured in volts.

Problem 3

A battery gives 50 J of energy to 10 C of charge. Find the voltage.
Answer and explanation

5 V

V = W ÷ Q = 50 ÷ 10 = 5 V.

Problem 4

Making a wire longer, with everything else the same, will:
  1. have no effect on its resistance
  2. turn it into an insulator
  3. decrease its resistance
  4. increase its resistance
Answer and explanation

increase its resistance

Resistance increases with length, since charge must travel through more material.

Problem 5

A current of 3 A flows for 4 seconds. How much charge passes?
Answer and explanation

12 C

Q = I × t = 3 × 4 = 12 C.

Problem 6

Explain the difference between voltage and current, using an analogy of your choice.
Answer and explanation

Current is the amount of charge flowing per second, while voltage is the push that drives that flow — the energy given to each unit of charge. In a water analogy, current is like the amount of water flowing through a pipe each second, and voltage is like the pressure from the pump that pushes the water. Voltage is the cause; current is the resulting flow.

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