Electricity and Circuits — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. You rub a balloon on a wool sweater. The balloon gains extra electrons. What charge does the balloon now have?
A) positive
B) negative
C) neutral
D) no charge at all
Electrons carry a negative charge, so when the balloon picks up extra electrons from the wool, it ends up with more negative charges than positive ones, making its overall charge negative.
2. Which action would be the MOST dangerous around electricity?
A) turning off a light switch before changing a bulb
B) using a plug with a plastic handle
C) touching a frayed cord with wet hands
D) unplugging a device by pulling the plug
A frayed cord exposes live wires, and wet hands lower your skin's resistance, making it much easier for a dangerous amount of current to flow through your body.
3. A student connects a battery, a switch, and two bulbs in series. She opens the switch. What happens?
A) only the first bulb turns off
B) only the second bulb turns off
C) both bulbs turn off
D) both bulbs get brighter
In a series circuit all devices share one single path, so opening the switch breaks that path and stops current from reaching either bulb.
4. Lightning rods are placed on tall buildings. Why are they made of metal?
A) metal is a good insulator that blocks lightning
B) metal is shiny so lightning can see it
C) metal is a good conductor that safely carries the charge to the ground
D) metal is lightweight and easy to attach
Metal conducts electricity very well, so a metal lightning rod gives the massive charge from lightning a safe, low-resistance path straight down into the ground instead of through the building.
Part B: Fill in the Blank
Write the correct answer on each line.
1. A material through which electricity cannot flow easily is called an insulator.
Insulators hold their electrons tightly in place, which prevents current from flowing through. That is why rubber coating on wires keeps electricity safely inside.
2. Static electricity is caused by an imbalance of positive and negative charges on an object.
When an object gains or loses electrons, the balance between positive and negative charges is disrupted, creating static electricity on the object's surface.
3. A grounding wire carries excess electricity safely into the ground.
The earth can absorb huge amounts of electrical charge without harm, so a grounding wire directs dangerous excess electricity into the ground where it spreads out safely.
4. When you walk across carpet in socks, your body builds up a static charge.
Your socks rubbing against the carpet fibers transfer electrons to your body, building up a static charge that you feel as a zap when you touch something metal.
5. The three-prong plug on some appliances includes a grounding pin for safety.
The third prong connects to a grounding wire that sends stray electricity into the earth, protecting you from a shock if something goes wrong inside the appliance.