Worksheet: Radiation Pressure on Perfectly Reflective Surfaces

In this worksheet, we will practice calculating the pressure exerted on an object by light that is reflected by it.

Q1:

Which of the lines on the graph shows how the pressure exerted by radiation being reflected by a surface varies with the intensity of the radiation?

  • AThe blue line
  • BThe purple line
  • CThe green line
  • DThe orange line
  • EThe black line

Q2:

Light with an intensity of 50.0 W/m2 is directed at a 100% reflective surface. The surface has an area of 2.25 m2. What force is exerted by the light on the surface? Use a value of 3.00×10 m/s for the speed of light in a vacuum.

  • A7.50×10 N
  • B3.75×10 N
  • C1.67×10 N
  • D3.33×10 N
  • E1.48×10 N

Q3:

Light of constant intensity is directed at a 100% reflective surface. The light strikes the surface at an angle, as shown in the diagram. If 𝜃<90, will the radiation pressure exerted by the light on the surface be greater than, less than, or equal to the radiation pressure when 𝜃=90?

  • AEqual to
  • BLess than
  • CGreater than

Q4:

A large asteroid is on a collision course with Earth. The asteroid has a mass of 300,000 kg. The asteroid can be deflected if a 0.010 N force can be applied to it for 2.0×10 s. If a powerful laser is used to shine light on a 12 m2 area of the asteroid, what is the intensity of light needed in order to deflect the asteroid using radiation pressure? Assume that the surface of the asteroid is 100% reflective. Use a value of 3.00×10 m/s for the speed of light in vacuum. Give your answer in scientific notation to one decimal place.

  • A3.6×10 W/m2
  • B2.5×10 W/m2
  • C2.5×10 W/m2
  • D8.3×10 W/m2
  • E1.3×10 W/m2

Q5:

Light with an intensity of 60 W/m2 is directed at a 100% reflective surface. What is the pressure exerted by the light on the surface? Use a value of 3×10 m/s for the speed of light in vacuum.

  • A1×10 N/m2
  • B4×10 N/m2
  • C1.2×10 N/m2
  • D2.4×10 N/m2
  • E2×10 N/m2

Q6:

The diagram shows a 100% reflective surface that is parallel to light rays with a constant intensity of 40 W/m2. The thickness of the surface is negligible. What is the radiation pressure on the surface due to the light?

Q7:

The diagram shows an artist’s conception of a solar sail. A solar sail is a thin, light, highly reflective sheet that can be used as a method of propulsion for spacecraft. The solar sail reflects light from a nearby star; a net force is exerted on the sail due to radiation pressure.

If a spacecraft powered by a solar sail sets sail from Earth, traveling away from the Sun, what area would the solar sail have to have in order for the force exerted on it due to radiation pressure to be 1.00 N? The intensity of light from the Sun on Earth is 1,350 W/m2. Assume that all of the light that hits the sail is reflected. Use a value of 3.00×10 m/s for the speed of light in vacuum.

Solar sail
  • A1.11×10 m2
  • B4.44×10 m2
  • C6.75×10 m2
  • D2.22×10 m2
  • E1.35×10 m2

Q8:

Light from two lasers is directed at a 100% reflective surface. Laser A produces light with a wavelength of 500 nm, and laser B produces light with a wavelength of 700 nm. Both lasers produce the same number of photons per second. Which laser produces light that exerts a greater force on the surface?

  • ALaser B
  • BLaser A

Q9:

What intensity of light would be needed to exert a 1.0 N force on a polished copper plate with an area of 2.5 m2? Assume that all of the light incident on the copper plate is reflected. Use a value of 3.00×10 m/s for the speed of light in vacuum.

  • A3.0×10 W/m2
  • B6 W/m2
  • C2.4×10 W/m2
  • D1.2×10 W/m2
  • E3.8×10 W/m2

Q10:

Light is directed at a 100% reflective surface. The surface has an area of 4.00 m2. The light exerts a force of 2.00×10 N on the surface. What is the intensity of the light? Use a value of 3.00×10 m/s for the speed of light in vacuum.

  • A1,200 W/m2
  • B600 W/m2
  • C150 W/m2
  • D300 W/m2
  • E75 W/m2

Q11:

Light is directed at a 100% reflective surface. The light exerts a pressure of 3.50×10 N/m2 on the surface. What is the intensity of the light? Use a value of 3.00×10 m/s for the speed of light in vacuum.

  • A525 W/m2
  • B1,050 W/m2
  • C263 W/m2
  • D58.3 W/m2
  • E2,100 W/m2

Q12:

The diagram shows a 100% reflective surface that is struck by light of constant intensity. The surface has a negligible thickness, and it is rotating at a constant angular velocity. Which of the following graphs shows how the radiation pressure on the surface varies with time?

  • A
  • B
  • C
  • D
  • E

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