Practice Intensity in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

Wave intensity is the power carried by a wave through each unit of area.

Intensity tells you how concentrated the wave's energy flow is.

Showing a random 20 of 50 problems.

Example 1

medium

Source A and B emit equal power. You stand 3 m from A and 6 m from B. Which sounds more intense and by what factor?

Example 2

medium

Intensity at

2\,\text{m}

from a point source is

12\,\text{W/m}^2

. Find intensity at

8\,\text{m}

Example 3

easy

A speaker emits 12 W of sound power spread evenly over an area of 4 m^2. What is the intensity?

Example 4

easy

A wave delivers 50 W through a window of area 2 m^2. Find the intensity.

Example 5

hard

A point source has intensity

9\,\text{W/m}^2

4\,\text{m}

. At what distance is the intensity

1\,\text{W/m}^2

Example 6

challenge

A point source's intensity at distance

r

I_0

. By what factor must you increase

r

to reduce intensity to

I_0/100

Example 7

medium

A wave's intensity is 12 W/m^2 over a circular detector of radius 1 m (

A=\pi r^2

). How much power does it collect?

Example 8

medium

The intensity 2 m from a point source is 9 W/m^2. What is the intensity at 6 m?

Example 9

challenge

Two identical isotropic sources, each

40\,\text{W}

, sit

8\,\text{m}

apart. Find the total (incoherent) intensity at the midpoint (

A = 4\pi r^2

Example 10

challenge

A source radiates 100 W into a cone covering 1/10 of a full sphere. Find the intensity at 3 m. (Full sphere area

4\pi r^2

Example 11

hard

For a wave on a stretched string, intensity is proportional to amplitude squared. If amplitude triples (same frequency, medium), how does intensity change?

Example 12

easy

A loudspeaker outputs

20\,\text{W}

of sound power spread evenly over an area of

10\,\text{m}^2

. Find the intensity.

Example 13

medium

A point source emits

500\,\text{W}

. Find the intensity at

10\,\text{m}

(

A = 4\pi r^2

Example 14

medium

A source gives intensity 16 W/m^2 at 3 m. At what distance is the intensity 4 W/m^2?

Example 15

medium

3\,\text{m}

from a point source the intensity is

8\,\text{W/m}^2

. Find the source's total power (

A = 4\pi r^2

Example 16

medium

Intensity at

5\,\text{m}

from a point source is

4\,\text{W/m}^2

. At what distance is the intensity

1\,\text{W/m}^2

Example 17

medium

At 4 m a source gives 2 W/m^2. What total power does the source emit? (

A=4\pi r^2

Example 18

easy

If the area receiving a wave doubles while power stays the same, intensity ____.

Example 19

easy

Intensity of a wave is 8 W/m^2 over an area of 5 m^2. What total power passes through?

Example 20

hard

A speaker radiates

25\,\text{W}

uniformly into a forward hemisphere (

A = 2\pi r^2

). Find the intensity at

5\,\text{m}

on-axis.

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