### Multiple Choice

#### 15.1 The Electromagnetic Spectrum

Which type of EM radiation has the shortest wavelengths?

- gamma rays
- infrared waves
- blue light
- microwaves

Which form of EM radiation has the most penetrating ability?

- red light
- microwaves
- gamma rays
- infrared radiation

#### 15.2 The Behavior of Electromagnetic Radiation

To compare the brightness of light bulbs for sale in a store, you should look on the labels to see how they are rated in terms of ____.

- frequency
- watts
- amps
- lumens

What is the wavelength of red light with a frequency of 4.00 × 10^{14} Hz?

- 2.50 × 10
^{14}m - 4.00 × 10
^{15}m - 2.50 × 10
^{6}m - 4.00 × 10
^{-7}m

What is the distance of one light year in kilometers?

- 2.59 × 10
^{10}km - 1.58 × 10
^{11}km - 2.63 × 10
^{9}km - 9.46 × 10
^{12}km

How does the illuminance of light change when the distance from the light source is tripled? Cite the relevant equation and explain how it supports your answer.

- $\text{Illuminance=}\frac{P}{\text{4}\pi {r}^{\text{2}}}\text{;}$ if distance is tripled, then the illuminance increases by 19 times.
- $\text{Illuminance=}\frac{P}{\text{4}\pi r}\text{;}$ if distance is tripled, then the illuminance decreases by 13 times.
- $\text{Illuminance=}P\text{\xb74}\pi {r}^{\text{2}}\text{;}$ if distance is tripled, then the illuminance decreases by 9 times.
- $\text{Illuminance=}P\text{\xb74}\pi r\text{;}$ if distance tripled, then the illuminance increases by 3 times.

A light bulb has an illuminance of 19.9 lx at a distance of 2 m . What is the luminous flux of the bulb?

- 500 lm
- 320 lm
- 250 lm
- 1,000 lm