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In this lesson, we will learn how to calculate the energy, power, and intensity of electromagnetic waves and the magnitude of the Poynting vector.

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?

Q2:

At the top of Earth’s atmosphere, the time-averaged Poynting vector associated with sunlight has a magnitude of 1.40 kW/m^{2}.

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?

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.

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.

What is the peak electric field strength of the microwave?

What is the peak magnetic field strength of the microwave?

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