Question

# The light from a red laser pointer has a wavelength of about 600 nm. If this...

The light from a red laser pointer has a wavelength of about 600 nm. If this laser has a power of 0.18 mW, what is the momentum carried by a 1.8-s pulse of this radiation? (in kg · m/s)

The magnetic field associated with an electromagnetic wave has an amplitude of 1.6 μT.

(a) What is the amplitude of the electric field associated with this wave? (in V/m)

(b) What is the intensity of this wave? (W/m2)

(c) What is the radiation pressure associated with this wave? (N/m2)

(d) How much momentum is carried by a 1.3-s pulse of this wave over an area of 16 m2? (kg · m/s)

We know that, E = p c

where, c = speed of light = 3 x 108 m/s

(0.18 x 10-3 J/s) (1.8 s) = p (3 x 108 m/s)

p = (0.324 x 10-3 J) / (3 x 108 m/s)

p = 0.108 x 10-11 kg.m/s

p = 1.08 x 10-12 kg.m/s

(a) What is the amplitude of the electric field associated with this wave?

using a formula, we have

E0 = c B0 (3 x 108 m/s) (1.6 x 10-6 T)

E0 = 4.8 x 102 V/m

E0 = 480 V/m

(b) What is the intensity of this wave?

using a formula, we have

I = (c 0 E2) / 2

I = [(3 x 108 m/s) (8.85 x 10-12 C2/Nm2) (480 V/m)2] / 2

I = 305.8 W/m2

(c) What is the radiation pressure associated with this wave?

using a formula, we have

Prad = I / c = (305.8 W/m2) / (3 x 108 m/s)

Prad = 101.9 x 10-8 N/m2

Prad = 1.02 x 10-6 N/m2

(d) How much momentum is carried by a 1.3-s pulse of this wave over an area of 16 m2?

using a formula, we have p = Prad A t = (1.02 x 10-6 N/m2) (16 m2) (1.3 sec) p = 2.12 x 10-5 kg.m/s