Chapter 6

Questions :

1.What is a wave? Using a diagram, define the following terms associated with waves: wavelength, frequency, amplitude.

A wave can be described as a disturbance that travels through a medium from one location to another location

A wavelength is the distance between two identical points

A frequency is the number of waves that pass through an identical point in one second

Amplitude is the vertical distance from the middle of the wave to the top of a peak or to a bottom of trough .

For more clarity , look at the following diagram :

2.What are the units for wavelength and frequency of electromagnetic waves? What is the speed of light in meters per second and miles per hour?

The units for wavelength is m and for frequency is 1/s 

The speed of light in meters per second is :
$$s=3\times 10^8 \frac{m}{sec}$$

The speed of light in mile per second is :
$$33\times 10^8 \times \frac{3600}{1609}=6.71 mile/hour$$

3.List the types of electromagnetic radiation, starting with the radiation having the longest wavelength and ending with the radiation having the shortest wavelength.

Radio waves - microwaves - infrared waves - optical waves - ultraviolet waves - 

4. Give the high and low wavelength values that define the visible region of the electromagnetic spectrum.

A human =eye will respond to wavelengths from 390 to 750 nm .

5. (a) What is the wavelength (in nm) of light having a frequency of 8.6 × 10^13 Hz?
(b) What is the frequency (in Hz) of light having a wavelength of 566 nm?

a)
$$c=\lambda f$$
$$\lambda=\frac{c}{f}$$
$$c=3\times 10^8 meter/second$$
$$f=8.6 \times 10^13$$
$$\lambda = \frac{3\times 10^8}{8.6 \times 10^{13}}=3.5 \times 10^{-6}m$$

b)
$$c=\lambda f$$
$$f=\frac{c}{wavelength}$$
$$c=3\times 10^8 meter/second$$
$$\lambda =566 \times 10^{-9}$$
$$\lambda = \frac{3\times 10^8}{566 \times 10^{-9}}=3.5 \times 10^{-6}m$$

6.How many minutes would it take a radio wave to travel from the planet Venus to Earth? (The average distance from Venus to Earth = 28 million miles.) How long would it take an infrared wave to travel the same distance?

$$S_{light}=\frac{d}{t}$$
$$t=\frac{d}{S}$$
$$t=\frac{28\times 10^6 \times 1609 m}{3\times 10^{8}}$$
$$t=150 second \times \frac{1 min}{60 sec}=2.5 minute$$

7.The average distance between Mars and Earth is about 1.3 × 10^8 miles. How long would it take video images transmitted from the Mars Spirit rover on Mars' surface to reach Earth (1 mile = 1.61 km)?

$$S_{light}=\frac{d}{t}$$
$$t=\frac{d}{S}$$
$$t=\frac{1.3\times 10^8 \times 1610 m}{3\times 10^{8}}$$
$$t=697second \times \frac{1 min}{60 sec}=11.6 minute$$

8.Four waves represent light in four different regions of the electromagnetic spectrum: visible, microwave, infrared, and ultraviolet. Determine the best match of regions to the waves shown here. Explain your choices.

a) is an infrared wave .
b) is a visible wave .
c) is an ultraviolet wave .
d) is a radio wave .

9.A photon has a wavelength of 705 nm. Calculate the energy of the photon in joules.

$$E=hf$$
$$h=6.63\times 10^{-34}$$
$$f=c/wavelength$$
$$f=\frac{3\times 10^8}{705\times 10^{-9}=4.25\times 10^{14}}$$
$$E=4.25\times 10^{14} \times 6.63\times 10^{-34}=2.81\times{-19}$$

10.