Electricity and Circuits — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A student tests four materials to see which completes a circuit and lights a bulb. Which material will most likely work?
A) a wooden stick
B) a plastic straw
C) an iron nail
D) a rubber eraser
Iron is a metal, and metals are conductors that allow electrons to flow freely. A metal nail completes the circuit path so current can reach the bulb and light it.
2. Three bulbs are connected in parallel to a battery. One bulb is unscrewed. What happens to the other two?
A) they both go out
B) they stay on at the same brightness
C) they get dimmer
D) the battery stops working
Each bulb in a parallel circuit has its own separate path to the battery, so removing one bulb does not affect the other two -- they keep receiving the same voltage and shine just as brightly.
3. Why does a thick copper wire have less resistance than a thin copper wire of the same length?
A) thick wire weighs more so electrons move faster
B) thick wire gives electrons more room to flow
C) thin wire is a better conductor than thick wire
D) thick wire has fewer electrons inside it
A thicker wire has a larger cross-section, giving electrons more room to pass through at the same time, which reduces how much the wire resists the flow of current.
4. A circuit has a battery and a buzzer, but the buzzer does not make a sound. Which change would most likely fix the problem?
A) add another buzzer in series
B) replace the copper wire with a string
C) close the open switch in the circuit
D) remove the battery from the circuit
An open switch creates a gap that stops current from flowing. Closing the switch completes the circuit path so electricity can reach the buzzer and make it produce sound.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When two batteries are placed in series, the total voltage is the sum of both batteries' voltages.
Batteries in series stack their voltages, so a 1.5V battery plus another 1.5V battery gives a total of 3V -- the sum of both.
2. An electric fan converts electrical energy into mechanical energy that moves air.
The fan's motor turns electrical energy into the spinning motion of the blades, which is mechanical energy that pushes air around the room.
3. In a circuit diagram, an X inside a circle is the symbol for a bulb.
The X inside a circle represents the filament crossing inside a light bulb, which is why this symbol is used in circuit diagrams to show where a bulb is connected.
4. Materials like glass, rubber, and plastic are common insulators used to protect people from electricity.
Glass, rubber, and plastic all hold their electrons tightly, which blocks current from passing through and makes them excellent insulators for protecting people from electric shock.
5. Adding more devices in a series circuit increases the total resistance and decreases the current.
Each device added to a series circuit increases total resistance, and higher resistance means fewer electrons can flow per second, so the current decreases.