Electricity and Magnetism — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
when the switch is open the bulb lights up.
Corrected: When the switch is open, the bulb does not light up.
An open switch breaks the circuit so no current flows, and every sentence must start with a capital letter.
2. Fix the sentence:
a cut wire still carry electricity to the bulb.
Corrected: A cut wire does not carry electricity to the bulb.
Cutting the wire opens the circuit, and the singular subject wire needs the verb does, not carry.
3. Fix the sentence:
closed circuits has a complete path for current.
Corrected: A closed circuit has a complete path for current.
The singular noun circuit takes has, and the sentence needs the article a at the start for clarity.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A complete loop that lets current flow is called a closed circuit.
A closed circuit is a complete loop of conductors that lets electric current travel from the power source and back.
2. When a wire is cut, the circuit becomes open and the bulb turns off.
A cut wire creates a gap, so the circuit is open and current cannot flow to light the bulb.
3. A switch is a part that opens or closes a circuit when you flip it.
A switch is a device that makes or breaks the conducting path in a circuit to control the flow of current.
4. A battery is a power source that pushes current through the circuit.
A battery is called a power source because it supplies the energy that pushes charges around the circuit.
Part C: True or False?
Read each statement. Circle True or False.
1. Grade 3 fact: a closed circuit has no breaks and lets current flow.
True False
A closed circuit forms a continuous loop, so current can travel all the way from the battery and back.
2. Grade 3 fact: when the switch is open, the bulb still lights up.
True False
An open switch breaks the loop, so no current reaches the bulb and it stays dark.
3. Grade 3 fact: cutting a wire in a circuit stops the current from flowing.
True False
Cutting a wire opens the circuit and creates a break that current cannot jump across, stopping the flow.