Electricity and Circuits — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Static electricity happens when protons move from one object to another by rubbing.
Corrected: Static electricity happens when electrons move from one object to another by rubbing, causing one object to become negatively charged and the other positively charged.
Protons are locked inside the nucleus and cannot move between objects. It is the electrons on the surface that transfer when you rub two things together, creating static electricity.
2. Fix the sentence:
A switch must stay closed for a circuit to stop working and turn off a light.
Corrected: A switch must be opened to break the circuit and turn off a light; closing the switch allows electricity to flow again.
Opening a switch creates a gap in the circuit, which stops electricity from flowing and turns the light off. Closing the switch reconnects the path so current can flow again.
3. Fix the sentence:
In a parallel circuit, if one light bulb burns out, all the other bulbs go out too.
Corrected: In a parallel circuit, if one light bulb burns out, the other bulbs stay on because each bulb has its own separate path for electricity.
In a parallel circuit each bulb has its own path, so if one burns out the others keep working. It is a series circuit where all bulbs share one path and go out together.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. When you shuffle your feet on carpet and then touch a doorknob, you feel a shock from static electricity.
Shuffling your feet on carpet rubs electrons off the carpet onto your body, building up a static charge. Touching a doorknob releases that charge all at once as a small shock.
2. Every circuit needs an energy source, wires, and a load such as a bulb or motor.
The load is the part of the circuit that uses the electricity to do useful work, like a bulb producing light or a motor spinning a fan.
3. Objects with the same electrical charge repel each other.
Like charges push away from each other -- two negatively charged objects repel because their extra electrons create a force that drives them apart.
4. A battery is a device that stores chemical energy and converts it to electrical energy.
Inside a battery, chemicals react to release energy in the form of electricity. When those chemicals are used up, the battery dies and can no longer power a circuit.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Why does a balloon stick to a wall after you rub it on your hair?
Sample answer: Rubbing the balloon on your hair transfers electrons to the balloon, giving it a negative charge. The charged balloon attracts the positive charges in the wall, which makes it stick.
Rubbing transfers electrons from your hair to the balloon, giving it a negative charge. The negatively charged balloon then pulls toward the positive charges in the wall, making it stick.
2. Describe what happens inside a flashlight when you flip the switch to the ON position.
Sample answer: Flipping the switch closes the circuit, creating a complete path from the battery through the wires to the bulb and back. Electricity flows through the bulb, which converts the electrical energy into light.
Flipping the switch to ON closes the circuit so electricity travels from the battery through the wires to the bulb and back. The bulb's filament heats up and glows, converting electrical energy into light.