Electricity & Simple Circuits — Drills · Grade 8 Science

Chapter: Energy & Heat Transfer

What these drills covers

By the end of Electricity & Simple Circuits you should be able to:

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

Vocabulary used: circuit, current, voltage, resistance, series circuit, parallel circuit, model, evidence, system boundary, assumption.

Problem 1

For current to flow, a circuit must be
  1. open
  2. complete
  3. made of insulators
  4. at high temperature
Answer and explanation

complete

A complete conducting loop from one terminal of the source to the other is required.

Problem 2

Using V = IR, what current in amperes flows when 12 V is applied across 4 Ω?
Answer and explanation

3 A

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

Problem 3

What voltage in volts drives 0.5 A through a 20 Ω resistor?
Answer and explanation

10 V

V = IR = 0.5 × 20 = 10 V.

Problem 4

A 9 V supply drives 0.3 A. What is the resistance in ohms?
Answer and explanation

30 Ω

R = V/I = 9/0.3 = 30 Ω.

Problem 5

In a series circuit, if one bulb is removed
  1. the others stay lit
  2. the whole circuit stops
  3. the current doubles
  4. nothing changes
Answer and explanation

the whole circuit stops

A series circuit has one path, so breaking it anywhere stops the current everywhere.

Problem 6

Two identical bulbs in parallel compared with the same two in series are
  1. dimmer
  2. brighter
  3. identical
  4. unlit
Answer and explanation

brighter

Each parallel bulb receives the full supply voltage, so more current flows through each.

Problem 7

Explain why household circuits are wired in parallel rather than in series.
Answer and explanation

In parallel each appliance receives the full supply voltage and can be switched on or off independently, and a failure in one does not interrupt the others. In series every device would share the voltage, so they would run poorly, and a single failure or switch would cut power to everything on the circuit. Parallel wiring also lets each branch carry only the current its own device needs.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

A circuit is built correctly but nothing lights. List three things to check and why each matters.
Answer and explanation

Check that the loop is complete, since any gap or loose connection stops the current. Check the cell's polarity and whether it still has charge, since a flat or reversed source supplies no useful current. Check the component itself — a blown bulb filament breaks the path even though the wiring looks right. Testing one change at a time keeps it clear which fault was responsible.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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