Physics Quiz

Which instrument measures the electric current flowing in a circuit?

• Voltmeter
• Ammeter
• Barometer
• Ohmmeter

Answer: Ammeter. An ammeter measures current in amperes and is connected in series. A voltmeter measures potential difference and is connected in parallel, and an ohmmeter measures resistance.

A pencil standing in a glass of water looks bent at the water's surface. What causes this?

• Reflection
• Diffraction
• Refraction
• Dispersion

Answer: Refraction. Light changes speed as it passes from water into air, and it bends. This bending is refraction, and it makes the part under water look shifted.

Which colour of visible light has the longest wavelength?

• Violet
• Green
• Blue
• Red

Answer: Red. Red has the longest wavelength we can see, about 700 nanometres. Violet has the shortest, about 400 nanometres.

Why does the clear daytime sky look blue?

• Sunlight reflects off the oceans
• Air molecules scatter blue light more than red
• The ozone layer is blue
• Water vapour absorbs every other colour

Answer: Air molecules scatter blue light more than red. Tiny air molecules scatter short wavelengths far more strongly than long ones (Rayleigh scattering), so scattered blue light reaches our eyes from every part of the sky.

A thermos flask keeps tea hot for hours. What does most of the work?

• A vacuum between two walls
• A thick plastic outer case
• A layer of ice in the lid
• A small heating coil

Answer: A vacuum between two walls. Heat cannot cross a vacuum by conduction or convection. The shiny inner walls also reflect heat back in, which cuts the loss by radiation.

On the Moon in 1971, Apollo 15 astronaut David Scott dropped a hammer and a feather at the same moment. What happened?

• The hammer landed first
• The feather floated away
• They landed together
• The feather landed first

Answer: They landed together. The Moon has no air, so there was no air resistance, and both fell at the same rate, as Galileo had predicted. On Earth, air slows the feather down.

Which of these is a scalar quantity?

• Velocity
• Force
• Displacement
• Speed

Answer: Speed. A scalar has size only. Speed is a scalar; velocity is speed with a direction, which makes it a vector, like force and displacement.

Which inventor came up with the unit 'horsepower' to sell his steam engines to mill owners who used horses?

• James Watt
• Thomas Edison
• George Stephenson
• Nikola Tesla

Answer: James Watt. James Watt compared his engines with working horses. The SI unit of power, the watt, is named after him, and 1 horsepower is about 746 watts.

At what temperature do the Celsius and Fahrenheit scales show the same number?

• 0
• -40
• 100
• -273

Answer: -40. F = (9/5 x C) + 32. Put F = C and solve, and you get C = -40. So -40°C is exactly -40°F.

Astronauts float inside the International Space Station, about 400 km above Earth. Why?

• There is no gravity at that height
• The station's walls block gravity
• They and the station are falling around Earth together
• Air pressure inside lifts them up

Answer: They and the station are falling around Earth together. Gravity at the station's height is still about 90% as strong as on the ground. The station and the crew are in constant free fall around Earth, so nothing presses them to the floor.