Q: Two identical 1.00 g spheres are placed 2.00 cm apart and released from rest. Each accelerates at $$225\ \text{m/s}^2. $$What is the magnitude of the charge on each sphere?

$$1.0 \times 10$$^{-7}$$\ \text{C}$$

Question 1

A machine emits a persistent 80 Hz hum and is located 5.0 m from a worker. To cancel the noise at the worker’s location using a loudspeaker that duplicates the hum, how far from the worker should the speaker be placed? (Speed of sound = 340 m/s)

Accepted Answer

$$2.9\ 	ext{m}$$

Question 2

What is the wavelength of an 80 Hz sound wave in air if the speed of sound is $$340\ 	ext{m/s}$$?

Accepted Answer

$$2.125\ 	ext{m}$$

Question 3

Refer to the first image (circular wave fronts). At point Q, the path difference $$\Delta r$$ between the two sources is $$\frac{3}{2}\lambda. $$What type of interference occurs at Q?

Accepted Answer

Destructive interference

Question 4

For two in-phase sound sources, constructive interference occurs at points where the path difference $$\Delta r is$$:

Accepted Answer

$$\Delta r = m\lambda,\ m=0,1,2,...$$

Question 5

Two identical loudspeakers are 2.0 m apart and emit 1800 Hz sound waves. At a point 4.0 m directly in front of one speaker (see second image), what type of interference occurs? (Speed of sound = 340 m/s)

Accepted Answer

Perfect destructive interference

Question 6

Calculate the wavelength of a 1800 Hz sound wave in air if the speed of sound is $$340\ 	ext{m/s}.$$

Accepted Answer

$$0.1889\ 	ext{m}$$

Question 7

Refer to the third image (balls A, B, C, D). Ball A is touched by a plastic rod rubbed with wool. Balls B, C, and D are attracted to A. Balls B and D have no effect on each other. Ball B is attracted to C. What are the charge states of A, B, C, and D?

Accepted Answer

A: negative, B: neutral, C: positive, D: neutral

Question 8

In the fourth image (balls 1 and 2), which diagram (A-E) best represents the situation where both balls are touched by a negatively charged rod?

Accepted Answer

Diagram B

Question 9

In the fifth image (balls 1 and 2), which diagram (A-E) best represents the situation where ball 1 is touched by a negatively charged rod and ball 2 is touched by a positively charged rod?

Accepted Answer

Diagram C

Question 10

Refer to the sixth image (charges A, B, C). What is the net electric force on charge A due to charges B and C? ($$q_A = 1.0\ 	ext{nC}$$, $$q_B = -1.0\ 	ext{nC}$$, $$q_C = 4.0\ 	ext{nC}$$, distances as shown)

Accepted Answer

$$0\ 	ext{N}$$

Question 11

Two identical 1.00 g spheres are placed 2.00 cm apart and released from rest. Each accelerates at $$225\ 	ext{m/s}^2. $$What is the magnitude of the charge on each sphere?

Accepted Answer

$$1.0 	imes 10$$^{-7}$$\ 	ext{C}$$

Question 12

Which of the following best describes why two neutral conducting balls, when touched by a negatively charged rod, repel each other?

Accepted Answer

Both balls acquire negative charge and like charges repel.

Question 13

If two point charges $$q_1$$ and $$q_2$$ are separated by a distance $$r$$, what is the magnitude of the electrostatic force between them?

Accepted Answer

$$F = \frac{1}{4\pi\$$varepsilon_0$$} \frac{|q_1$ q_2$|}{r^2$}$$

Question 14

A neutral ball is attracted to a negatively charged rod. What is the best explanation for this attraction?

Accepted Answer

Charge polarization occurs in the neutral ball.

Question 15

If the path difference between two sound sources at a point is $$\lambda$$, what type of interference occurs at that point?

Accepted Answer

Constructive interference

Question 16

A speaker emits a sound of frequency $$f$$ and speed $$v. $$What is the formula for the wavelength $$\lambda$$?

Accepted Answer

$$\lambda = \frac{v}{f}$$

Physics Homework Guidance: Interference, Sound, and Electrostatics

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