Electricity and Magnetism — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Grade 3: In a circuit, one bulb lights up. If you add a second bulb in a simple loop with the same battery, what is most likely to happen?
A) Both bulbs glow a little dimmer
B) The first bulb glows twice as bright
C) The battery instantly becomes fully charged
D) Both bulbs will not light at all under any condition
Adding a second bulb in a single loop splits the battery's energy between them, so each bulb is a bit dimmer.
2. Grade 3: A student places a bar magnet near a pile of items. Which object will the magnet pull toward itself the most?
A) An iron paper clip
B) A rubber eraser
C) A wooden pencil
D) A piece of paper
Iron paper clips are magnetic; rubber, wood, and paper contain no magnetic metals so the magnet ignores them.
3. Grade 3: If you flip a switch from closed to open in a circuit with one bulb, what happens next?
A) The bulb turns off because the loop is broken
B) The bulb glows brighter than before
C) The battery starts to heat up the wires instantly
D) Nothing changes at all in the working circuit
Opening the switch creates a break, so current cannot complete the loop and the bulb shuts off.
4. Grade 3: Two bar magnets are slid toward each other with their north poles facing. What will you most likely feel and see?
A) They push apart and resist coming together
B) They snap tightly together right away
C) They spin around in a fast circle
D) They heat up until they glow brightly
Like poles repel, so two norths push apart; only opposite poles attract and snap together.
Part B: Fill in the Blank
Write the correct answer on each line.
1. If you cut a wire in the middle of a working circuit, the bulb will go out.
Cutting the wire opens the circuit and stops the current, so the bulb has no energy to glow.
2. Two south poles held close together will repel each other, not pull together.
Two south poles are like poles, and like poles always push away from each other because of magnetic force.
3. A magnet will not pick up a plastic button because plastic is non-magnetic.
Plastic buttons contain no iron or steel, so magnetic forces do not act on them.
4. Adding a second battery in the same direction to a circuit often makes the bulb glow brighter.
Two batteries together push more current through the bulb, so the filament heats up and shines more brightly.
5. When a compass is placed on a table far from metal, its needle points toward north.
The compass needle is a tiny magnet that lines up with Earth's magnetic field so one end points north.