PHYS106 HW Questions

When a laser beam is sent to the moon, reflected there, and returned to earth, it takes 2.5 seconds for the round trip. Calculate the distance to the moon.

1.25 to the moon, speed s = 3x10^8 m/s time = 1.25 sec d = speed x time = 3.75 x 10^8 m

To focus a camera, you move the lens back or forward. When the lens is closest to the film, are you focused on a near or far object?

Far object

(a) What is the critical angle? (b) Which pair of materials has the greater critical angle: air-water or air-diamond?

a. The critical angle is the angle where total internal reflection first happens. b. Air - water has a critical angle of about 42 degrees, while air - diamond has one of 24.5 degrees

(a) The speed of light in a certain glass is 200,000 km/sec. What is the index of refraction of this glass? (b) The index of refraction of a certain type of diamond is 2.5. What is the speed of light in this diamond?

a. n = c/v = 3e8 / 200,000 (1/1000) = 1.5 b. n = c/v = 2.5 v = c/2.5 = (3e8/2.5) = 1.2e8 m/s

Why did Etienne de Silhouette use a candle (point source) when making his silhouette tracings rather than a larger (and perhaps) brighter source?

To make a sharp shadow, all the light rays that are between the edges of the object must be blocked by the object. This can only be done with a point source.

Blue light bends more than red light when entering glass from air because: (a) red light travels faster than blue light in glass, (b) blue light travels faster than red light in glass, (c) red light travels faster than blue light in air, or (d) blue light travels faster than red light in air.

a. nred < nblue n = c/v (higher n means higher refraction)

In DC, radio station WRC broadcasts on AM at 980 kHz. Station WETA broadcasts on FM at 90.9 MHz. What are the wavelengths of the radio waves used in each case?

c = frequency x > speed = frequency x wavelength c = 3.0 x 10^8 m/s > = c/f WRC: f = 980 kHz > = 3e8/980e3 = 306 meters WETA: f = 90.9 MHz > =3e8/90.9e6 = 3.30meters

An exposure meter indicates that if a correct setting for a photograph is f/5.6 at 1/100 sec, then f/11 at 1/25 second is also correct for the same conditions. Give two other correct settings.

f/8 - 1/50 sec f/16 - 2/25 sec

Identify the type of electromagnetic radiation of each of the following wavelengths in a vacuum: 600 nm, 300 nm, 1400 nm, 21 cm, .1 nm, 3 km.

600: visible 300: UV 1400: IR 21: mircowave .1 : x-rays 3: radio

What is depth of field and how is it controlled in a camera?

DoF: range of distances over which objects will be in focus. It is controlled by the aperture. The smaller the aperture, the greater the depth of field.

A light wave traveling in the vacuum comes to a plate of glass. On entering the glass, which, if any, of the following increase, decrease, remain unchanged: the frequency of the wave, its wavelength, its speed?

Frequency: unchanged Wavelength & speed: decreased

What do you see when you look up while standing in the umbra? The penumbra? What would you see if you were standing on the moon, looking at the Earth? During a solar eclipse, some regions see a total eclipse, some a partial eclipse, and some no eclipse yet everyone sees a lunar eclipse the same way. Why?

If you are in the umbra, you will see the sun as a dark disc with a relatively faint glow around the edges. If you are in the penumbra, you will see rays from one side of the sun but not the other, making the sun appear crescent shaped. If you are on the moon, you would see a dark circle with a lighter shadow surrounding it. Solar eclipses are narrow. In a lunar eclipse, the Earth is blocking the Sun's rays making it visible to no one.

How do you measure wavelength of a wave?

Measure from top of one wave to another

As a black body becomes hotter, does it emit more or less radiation? Does it radiate predominantly at a higher or lower frequency?

The intensity increases with increasing temperature. The wavelength at which the peak intensity is emitted decreases with temperature.

A student, who obviously didn't read this book, had a van whose window he had covered with half-silvered mirrors. When he checked it out during the day, he assured himself that, while he could see out, no one could see in. That night he parked his van in a dark parking lot, climbed inside with his lantern and a friend, and enjoyed what he though was the privacy of his own home. A passing police officer saw him through the half-silvered mirrors and promptly busted him. Why could the police officer see in?

The police officer could see in because it is brighter inside the vehicle than outside when it is night.

In what direction can you see a rainbow early on a rainy morning? Why?

The west because the sun is east in the morning