In this worksheet, we will practice calculating the pressure due to incident radiation of a given intensity that is experienced by an object.

Q1:

A 150-W lightbulb emits of its energy as electromagnetic radiation. The bulb is at the center of a perfectly light absorbing sphere of radius 10.00 m. What is the radiation pressure on the sphere’s interior?

• A N/m2
• B N/m2
• C N/m2
• D N/m2
• E N/m2

Q2:

Sunlight falls perpendicularly on a kite with a reflecting surface of area 0.75 m2. The average intensity of the sunlight is 900 W/m2.

What is the average force on the kite due to radiation pressure?

• A N
• B N
• C N
• D N
• E N

If the kite material is black and absorbs all sunlight, what is the average force on the kite due to radiation pressure?

• A N
• B N
• C N
• D N
• E N

Q3:

A microscopic spherical dust particle of radius 2.000 μm and mass 10.0 µg is moving in outer space at a constant speed of 30.0 cm/s. A wave of light strikes the particle from the opposite direction to the direction of the particle’s motion and this light is absorbed. The particle decelerates uniformly to rest in a time of 1.00 s. What was the average electric field amplitude of the absorbed light?

• A V/m
• B V/m
• C V/m
• D V/m
• E V/m

Q4:

Electromagnetic radiation from a 5.00-mW laser is concentrated into a 1.00-mm2-area beam.

What is the radiation intensity of the beam?

• A W/m2
• B W/m2
• C W/m2
• D W/m2
• E W/m2

What is the maximum electric force that the beam can exert on a 2.00-nC electric charge?

• A N
• B N
• C N
• D N
• E N

What is the maximum magnetic force that the beam can exert on a 2.00-nC charge that has a speed of 400 m/s?

• A N
• B N
• C N
• D N
• E N

Q5:

A 150 W light bulb emits radiation with a power of 6.2 W uniformly in all directions. What pressure does the emitted radiation exert on a mirror at a distance of 1.0 m from the bulb?

• A Pa
• B Pa
• C Pa
• D Pa
• E Pa

Q6:

Sunlight reaches the ground with an intensity of 1.3 kW/m2. A sunbather has a body surface area of 1.0 m2 facing the sun while reclining on a beach chair on a clear day. His skin absorbs all the sunlight incident on it.

How much energy from direct sunlight reaches the sunbather’s skin per second?

What pressure does the absorbed sunlight exert on his skin?

• A Pa
• B Pa
• C Pa
• D Pa
• E Pa