Poynting Vector — Practice Quiz

Question 1

An EM wave in vacuum has E₀ = 100 V/m. The time-averaged intensity is:

Accepted Answer

13.3 W/m²

Answer

6.6 W/m²

Answer

26.6 W/m²

Answer

1.33 W/m²

Question 2

A 100 W isotropic lamp radiates uniformly. Intensity at 5 m is:

Accepted Answer

0.32 W/m²

Answer

0.16 W/m²

Answer

0.5 W/m²

Answer

1 W/m²

Question 3

If E₀ of an EM wave is doubled, the intensity becomes:

Accepted Answer

4×

Answer

Same

Answer

2×

Answer

8×

Question 4

The Poynting vector at a point in an EM wave gives:

Accepted Answer

Direction & magnitude of energy flow

Answer

Wavelength

Answer

Polarisation

Answer

Phase of B

Question 5

Solar intensity at Earth's orbit is 1.36 kW/m². The peak E-field of solar EM waves is:

Accepted Answer

≈ 1000 V/m

Answer

≈ 100 V/m

Answer

≈ 10 V/m

Answer

≈ 10000 V/m