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Lesson: Energy, Power, and Intensity of Electromagnetic Waves

Sample Question Videos

Worksheet • 12 Questions • 2 Videos

Q1:

A 150-W lightbulb emits 5 . 0 0 % of its energy as electromagnetic radiation. What is the magnitude of the average Poynting vector 10.0 m from the bulb?

  • A 5 . 9 7 × 1 0 3 W/m2
  • B 6 . 1 1 × 1 0 3 W/m2
  • C 5 . 5 9 × 1 0 3 W/m2
  • D 5 . 8 5 × 1 0 3 W/m2
  • E 5 . 7 4 × 1 0 3 W/m2

Q2:

At the top of Earth’s atmosphere, the time-averaged Poynting vector associated with sunlight has a magnitude of 1.40 kW/m2.

What is the maximum value of the electric field magnitude for a wave of this intensity?

What is the maximum value of the magnetic field magnitude for a wave of this intensity?

  • A 3 . 4 2 × 1 0 6 T
  • B 3 . 7 2 × 1 0 6 T
  • C 3 . 3 6 × 1 0 6 T
  • D 3 . 6 0 × 1 0 6 T
  • E 3 . 5 1 × 1 0 6 T

What is the total power radiated by the sun? Assume that the Earth is 1 . 5 0 × 1 0 1 1 m from the Sun and that sunlight is composed of electromagnetic plane waves.

  • A 3 . 9 6 × 1 0 2 6 W
  • B 5 . 5 9 × 1 0 2 6 W
  • C 2 . 1 6 × 1 0 2 6 W
  • D 4 . 7 7 × 1 0 2 6 W
  • E 3 . 0 3 × 1 0 2 6 W

Q3:

The specific heat capacity of spaghetti is 3 . 7 6 × 1 0 / 3 J k g C . 0.400 kg of spaghetti occupies a circular area 20.0 cm in diameter inside a microwave oven. On its highest power setting, the oven increases the temperature of the spaghetti by 4 5 . 0 C in 120 s.

What was the rate of energy absorption by the spaghetti, assuming that the spaghetti was perfectly absorbing?

Find the average intensity of the microwaves.

  • A 1 . 8 0 × 1 0 4 W/m2
  • B 2 . 6 3 × 1 0 4 W/m2
  • C 1 . 5 6 × 1 0 5 W/m2
  • D 2 . 3 3 × 1 0 4 W/m2
  • E 2 . 0 7 × 1 0 4 W/m2

What is the peak electric field strength of the microwave?

  • A 3 . 6 8 × 1 0 3 V/m
  • B 4 . 1 1 × 1 0 3 V/m
  • C 3 . 7 7 × 1 0 3 V/m
  • D 4 . 0 3 × 1 0 3 V/m
  • E 3 . 8 9 × 1 0 3 V/m

What is the peak magnetic field strength of the microwave?

  • A 1 . 2 3 × 1 0 5 T
  • B 1 . 4 4 × 1 0 5 T
  • C 1 . 2 9 × 1 0 5 T
  • D 1 . 4 0 × 1 0 5 T
  • E 1 . 3 5 × 1 0 5 T
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