Amplitude and Energy

Energy of a Wave

​Mr EP

​All waves carry energy. The energy of some waves, such as the energy of earthquakes, can be directly observed. Similarly, the churning of the shore by the water waves and loud sounds are manifestations of wave energy.

​Energy of Wave

​The amount of energy carried by a wave directly depends on its amplitude. A high amplitude defines a high energy wave. Likewise, a low energy wave is characterized by a low amplitude.

​The amount of energy carried by a wave directly depends on its amplitude.

​Wave Energy-Amplitude Relationship

​Wave Energy-Amplitude Relationship

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A wave transfers ​

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during the propagation

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What will happen happen to the wave energy if we double the amplitude?​ ​

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Multiple Choice

A system consists of a mass vibrating on the end of a spring. The total mechanical energy of this system?

• varies as a sine or cosine function.

• is constant only when the mass is at maximum displacement.

• is a maximum when the mass is at its equilibrium position only.

• is constant, regardless of the displacement of the mass from the equilibrium position.

Intensity

The intensity of a wave is defined as the rate of energy transmitted (power) per unit area at right angles to the wave velocity.

​I : intensity (W/m²)
P : Power (W)
A : Area (m²)

Intensity is defined equal to the amount of energy transferred per second divided by the area through which the energy passes.

​Image shows wave expanding our from a source. This shows an ideal source of sound energy. The energy spreads uniformly in all directions (spherical symmetry).

​Intensity

Multiple Choice

A 100 W lamp emits electromagnetic radiation in all directions. Assuming the lamp to be a point source, calculate the intensity of the radiation at a distance of 1.0 m from the lamp

• 25 W/m²

• $$\frac{25}{\pi}\ \frac{W}{m^2}$$

• $$25\pi\ \frac{W}{m^2}$$

• $$\frac{\pi}{25}\ \frac{W}{m^2}$$

Multiple Choice

A source of light emits electromagnetic wave. if an detector is located 5 m and measure intensity of wave I , what is measured intensity if it is located 10 m from source?

• 4I

• 2I

• 1/2 I

• 1/4 I

Intensity and Amplitude

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if one wave has twice the amplitude of another, it has ​

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times the intensity

Multiple Choice

A wave from a source has an amplitude of 5.0 cm and an intensity of 400 W m⁻². The amplitude of the wave is increased to 10.0 cm. Calculate the intensity now

• 800 w/m²

• 1600 W/m²

• 200 W/m²

• 100 W/m²

Multiple Choice

A wave from a source has an amplitude of 5.0 cm and an intensity of 400 W m⁻². The intensity of the wave is decreased to 100 W m⁻². Calculate the amplitude now

• 1.25 cm

• 2.50 cm

• 7.50 cm

• 10.0 cm