Atoms and Charges
This ancient Greek philosopher first proposed that matter is made of tiny "uncuttable" particles.
Democritus
The symbol for current is "I" and it is measured in this unit.
Amperes (A)
The mains voltage used in Hong Kong homes.
220 V
This thin wire melts to break a circuit when current gets dangerously high.
A fuse
In the water analogy of a circuit, the battery is compared to this device.
A water pump
This dramatic natural event in the sky is essentially a giant electrical discharge.
Lightning
Name the three subatomic particles found inside every atom.
Protons, neutrons, and electrons
This quantity, measured in volts, represents the energy given to each charge by a battery.
Voltage
Household sockets are wired in this configuration so every appliance receives the same voltage.
Parallel
Unlike a fuse, this safety device can simply be switched back on after it trips.
A circuit breaker
In the water analogy, the flow of water represents this electrical quantity.
The current
What is the largest mammal on Earth
Blue Whale
Of the three subatomic particles, this one is responsible for the flow of electricity in a wire.
The electron
Resistance is measured in this unit, written with the Greek letter ฮฉ.
Ohms
The brown wire in a UK/HK 3-pin plug has this job.
It is the live wire โ brings the voltage into the appliance
This green and yellow wire safely directs stray current away into the ground.
The earth wire
A lamp or appliance is often compared to this water-powered machine that converts flow into useful work.
A waterwheel
What gas do plants absorb from the air?
Carbon Dioxide
A neutral atom that loses two electrons will end up with this overall charge.
Positive (+2)
A circuit has a voltage of 12 V and a resistance of 6 ฮฉ. Calculate the current.
2 A (I = V รท R)
This blue wire in a plug provides the return path for the current.
The neutral wire
The hazard caused by plugging too many appliances into a single socket.
Overloading
In the "height" analogy, voltage corresponds to this physical quantity.
The height (or energy) difference
What is the smallest prime number?
2
Walking across a carpet and getting a small shock when touching a doorknob is caused by this.
A build-up of static charge / a discharge of accumulated electrons
A bulb has a current of 0.5 A flowing through it when 6 V is applied. What is its resistance?
12 ฮฉ
An electric kettle and a toaster both rely on this effect of an electric current.
The heating effect
The hazard where a stray wire bypasses the appliance, allowing current to flow with very little resistance.
A short circuit
Resistance is sometimes pictured as this material blocking the flow of water in a pipe.
Sand (or a sand filter)
Who painted the Mona Lisa?
Leonardo da Vinci
True or false: Rubbing two objects together creates new charges.
False โ it only transfers electrons from one object to the other
If the voltage in a circuit doubles while resistance stays the same, this happens to the current.
It also doubles
A washing machine drum and a vacuum cleaner both spin using this effect of an electric current.
The magnetic effect (electric motor)
A microwave normally draws 9 A. Choose the most appropriate fuse rating from 3 A, 5 A, or 13 A.
13 A โ must be slightly above normal current but not so high it fails to protect
Why scientists use analogies like water flow to teach electricity.
Because electricity is invisible and abstract โ comparing it to something familiar (like water) makes it easier to picture and understand
What is the chemical symbol for gold?
Au
Explain why a positively charged balloon can stick to a neutral wall.
The positive balloon pulls electrons in the wall surface closer, leaving a slight negative region on the wall that attracts the balloon
A heater is rated at 10 A and connected to the 220 V mains. Calculate its resistance and state the formula used.
22 ฮฉ, using R = V รท I
Explain why mains voltage at 220 V can be dangerous even though small batteries at 9 V are safe to touch.
The much higher voltage at 220 V can push enough current through the human body to cause severe shock, burns, or stop the heart, whereas 9 V cannot push enough current through the body's resistance to be harmful
Explain why fitting a 30 A fuse where a 5 A fuse is required is extremely dangerous.
The 30 A fuse will allow a much larger current to flow before melting, so the wires can overheat and start a fire, and the user is no longer protected from electric shock โ the safety purpose is defeated
Give one way the water-pump analogy can be misleading or break down when applied to real circuits.
Possible answers: water can leak out of pipes but charges do not leak out of wires; water needs to be supplied but charges already exist in the wire; the battery doesn't "make" electrons; voltage is not literally height โ any reasonable limitation accepted
This Serbian-American engineer championed alternating current (AC) and famously clashed with Thomas Edison during the "War of the Currents."
Nikola Tesla