How Does It Work? Quiz – Printable Version
20 multiple-choice questions with an explained answer key, ready to print.
Print the sheet (or save it as a PDF from the print window), hand it out, then mark it together using the answer page: every answer is explained. Perfect for a party, a birthday, a classroom, a care home or a team activity.
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- How does a speed camera radar measure a car's speed?
- A. Using the Doppler effect: the radio wave reflected by the car changes frequency according to its speed
- B. By photographing the number plate twice and comparing its size
- C. By measuring the heat given off by the engine
- D. By picking up the driver's phone GPS
- What does a lidar, used by self-driving cars and archaeologists, send out to 'see' in 3D?
- A. Ultrasound, like a bat
- B. Very low-frequency radio waves
- C. Laser pulses, whose return it times
- D. Low-dose X-rays
- Which animal naturally uses the same principle as a ship's sonar?
- A. The shark
- B. The octopus
- C. The dolphin
- D. The salmon
- Why doesn't light escape from an optical fibre, even when it is bent?
- A. It bounces off the inner wall by total internal reflection and cannot get out
- B. The fibre is coated with a thin metal mirror
- C. An air vacuum draws the light towards the centre
- D. It does escape, which is why fibres must never be bent
- Why does an induction hob stay barely warm while the water in the pan is boiling?
- A. The hob is cooled by an iced-water circuit
- B. It heats with microwaves, which only affect the water
- C. The glass top reflects the heat upwards
- D. The heat is generated directly in the base of the pan, not in the hob
- What liquid often drips from a small pipe under an air conditioner or an air-conditioned car?
- A. Water, from the air's moisture that has condensed
- B. Spent refrigerant
- C. Compressor oil
- D. Engine coolant
- Why doesn't setting the thermostat to 30 °C warm the room up any faster?
- A. Above 25 °C the heating goes into safety mode
- B. The thermostat measures high temperatures poorly
- C. The heating is already running at full power until the target temperature is reached
- D. Radiators heat less when the setting is high
- What is a seatbelt pretensioner for?
- A. To loosen the belt so the airbag can work
- B. To lock the buckle so it can't be undone
- C. To adjust the strap height automatically
- D. To tighten the belt within milliseconds of a crash, pinning the occupant to the seat
- Why do you pull away on a hill in first gear?
- A. It uses less fuel than the other gears
- B. It disengages the clutch to protect it
- C. It locks the differential for better grip
- D. It has the highest reduction: less speed but much more force at the wheels
- Why does electric power steering use less energy than old hydraulic steering?
- A. Its electric motor only works when you turn the wheel
- B. It runs on a small solar panel
- C. It only assists the driver when stationary
- D. It recovers braking energy to steer
- What does 'adaptive' cruise control do that standard cruise control doesn't?
- A. It chooses the route by itself
- B. It stops automatically at red lights
- C. It slows down and speeds up by itself to keep a safe distance from the vehicle in front
- D. It changes lanes to overtake
- What happens to an escalator's steps once they reach the top?
- A. They flatten out and travel back down upside down underneath, in a loop
- B. They fold up and are stored away
- C. They drop into a bin and are carried back up on a belt
- D. They go into the wall to be cleaned
- What do the digits printed under a product's barcode represent?
- A. The product's price in cents
- B. The date of manufacture
- C. The weight in grams
- D. The same number as the bars, in human-readable form, with a check digit
- How can an RFID badge or anti-theft tag work without a battery?
- A. It contains a micro-battery that lasts fifty years
- B. The reader's radio wave supplies the energy it needs to reply
- C. It recharges in light like a solar panel
- D. It runs on a permanent magnet
- Why does Wi-Fi struggle to get through an aquarium or a reinforced-concrete wall?
- A. Water and dense or metallic materials absorb or reflect radio waves
- B. Wi-Fi travels through the electrical cables in the walls
- C. Wi-Fi waves are light rays that only pass through glass
- D. The signal is deflected by the Earth's magnetism
- How do active noise-cancelling headphones 'erase' the drone of a plane?
- A. They replace the noise with louder music
- B. A foam filter absorbs all low sounds
- C. They produce an inverted sound wave that cancels the noise by interference
- D. They block the air in the ear canal
- What does an electric car's motor do when you lift your foot off the accelerator?
- A. It switches off and the car coasts without slowing
- B. It turns backwards to reverse
- C. It acts as a generator, slowing the car and recharging the battery
- D. It uses more energy to hold the speed
- Why does an alkaline battery eventually go 'flat'?
- A. The chemicals in its electrodes have been used up by the reaction
- B. It has emptied a small tank of stored electricity
- C. Air got in and stopped the reaction
- D. Its internal magnet has lost its magnetism
- Why are you advised not to leave a lithium-ion battery at 0% or in full sun?
- A. It might turn into an alkaline battery
- B. It would lose its 'memory' like older batteries
- C. It would become magnetic
- D. These conditions speed up its chemical wear and reduce its capacity
- How does an optical smoke detector spot the start of a fire?
- A. It 'smells' burning with a chemical nose
- B. Smoke particles scatter a light beam onto a sensor, which sets off the alarm
- C. It measures the room temperature
- D. It picks up the crackling of the fire
Answer key — How Does It Work? Quiz
- A. Using the Doppler effect: the radio wave reflected by the car changes frequency according to its speedThe faster the car, the more the frequency of the reflected wave differs from the one sent out, just as an ambulance siren changes pitch as it passes.
- C. Laser pulses, whose return it timesLidar fires hundreds of thousands of laser pulses a second and measures their round trip, producing a 3D 'point cloud'.
- C. The dolphinSonar sends out a sound and listens for its echo to locate the seabed or an obstacle; sound travels about 4 times faster in water than in air.
- A. It bounces off the inner wall by total internal reflection and cannot get outThe fibre's core has a higher refractive index than its cladding: beyond a certain angle, light is fully reflected and travels in a zigzag.
- D. The heat is generated directly in the base of the pan, not in the hobBeneath the glass, a coil creates a rapidly changing magnetic field that induces electric currents in the pan's metal base: that is what heats up.
- A. Water, from the air's moisture that has condensedAs it cools the air, air conditioning condenses the water vapour in it, like mist on a cold glass, so it also dries the air.
- C. The heating is already running at full power until the target temperature is reachedA thermostat compares the measured temperature with the setting and switches the heating accordingly.
- D. To tighten the belt within milliseconds of a crash, pinning the occupant to the seatA seatbelt always has a little slack, especially over a coat.
- D. It has the highest reduction: less speed but much more force at the wheelsA gearbox adjusts the ratio between engine speed and wheel rotation, exactly like the gears on a bike.
- A. Its electric motor only works when you turn the wheelThe old hydraulic pump was driven constantly by the engine, even in a straight line.
- C. It slows down and speeds up by itself to keep a safe distance from the vehicle in frontStandard cruise control holds a set speed by adjusting the throttle.
- A. They flatten out and travel back down upside down underneath, in a loopThe steps are attached to an endless chain. Guide rails make them flatten at each end, forming a landing, before they turn round under the machine.
- D. The same number as the bars, in human-readable form, with a check digitThe 13-digit EAN code identifies the product and the company; the last digit is a check digit that catches reading errors.
- B. The reader's radio wave supplies the energy it needs to replyA passive RFID tag contains a chip and an antenna. The reader sends out a radio field that 'wakes up' the chip and powers it just long enough to send back its ID.
- A. Water and dense or metallic materials absorb or reflect radio wavesThe 2.4 GHz band is close to a microwave oven's frequency, and water absorbs these waves well: an aquarium, or even a crowd of people, weakens the signal.
- C. They produce an inverted sound wave that cancels the noise by interferenceMicrophones pick up the ambient noise and the electronics generate the 'opposite' sound in real time: as one wave rises, the other falls, and they cancel out.
- C. It acts as a generator, slowing the car and recharging the batteryWith regenerative braking, some of the energy of motion is recovered instead of being lost as heat in the brakes.
- A. The chemicals in its electrodes have been used up by the reactionA battery doesn't store electricity: it contains reactants, zinc and manganese dioxide, whose reaction releases electrons.
- D. These conditions speed up its chemical wear and reduce its capacityIn a lithium-ion battery, lithium ions shuttle between two electrodes with every charge and discharge.
- B. Smoke particles scatter a light beam onto a sensor, which sets off the alarmInside a small dark chamber, an LED emits a beam that normally misses the sensor.