Electricity and Magnetism — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Grade 3: Why does a refrigerator magnet stick firmly to the fridge door but not to a wooden cabinet door?
A) The fridge door is made of steel, which contains magnetic iron
B) The wooden door is slippery and greasy on purpose
C) Magnets only work when the room is warm and sunny
D) All doors repel magnets except shiny ones
Steel contains lots of iron, which magnets attract strongly; wood has no magnetic metal so magnets ignore it.
2. Grade 3: Why does a compass needle always point toward the north when you let it settle?
A) Earth itself acts like a giant magnet with a north and south pole
B) The sun pulls on every compass during the day
C) Compasses contain tiny hidden batteries
D) Gravity pushes the needle sideways toward north
Earth has a magnetic field with poles, and a compass needle aligns its north end with Earth's magnetic north.
3. Grade 3: Electric eels can make strong electric shocks. Why does this ability help them survive?
A) They can stun prey and defend against predators
B) They use the shocks to change the color of rocks
C) Shocks make their scales grow faster each day
D) Electricity helps them read books under the water
Electric eels use quick bursts of electricity to stun fish they eat and to scare off animals that try to hunt them.
4. Grade 3: Why can an electromagnet in a junkyard crane drop a steel car exactly where the worker wants?
A) The current can be switched off to turn the magnet off
B) The car becomes lighter after being lifted up high
C) Steel melts when it is close to an electromagnet
D) Gravity reverses whenever the magnet is on
An electromagnet only pulls while current flows; cutting the current switches the magnetism off and drops the load.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Steel is attracted to magnets because it contains a lot of iron.
Steel is mostly iron mixed with carbon, and iron is strongly magnetic, so steel also responds to magnets.
2. Earth behaves like a giant magnet with its own north and south poles.
Movements inside Earth's core create a magnetic field that surrounds the planet and interacts with compasses.
3. An electric eel can give off shocks strong enough to stun fish.
Electric eels have special cells that store and release electric charge, producing shocks that stun prey.
4. An electromagnet only works while electric current flows through its wire.
The magnetic field of an electromagnet comes from moving charges; without current flowing, the magnetism disappears.
5. A compass needle points north because it lines up with Earth's magnetic field.
Earth's magnetic field reaches everywhere on the planet, and the compass needle rotates to match its direction.