Module 8 - CH 8 and 9 HW (Homework)

 

1)     The generator at a power plant produces AC at 27,000 V. A transformer steps this up to 355,000 V for transmission over power lines. If there are 2,050 turns of wire in the input coil of the transformer, how many turns must there be in the output coil?

       _________ turns

      2) What is the wavelength of the 62,500-Hz radio wave used by "radio-    controlled" clocks and wristwatches?

          _______ m

      3) A piece of iron is heated with a torch to a temperature of      743 K. How much more energy does it emit as blackbody       radiation at 743 K than it does at room temperature, 291   K?

          E₇₄₃

          E_{291   __________}

_{   Â} 

_{  4)}     What is the wavelength of the peak of the blackbody    radiation curve for the human body(T = 308 K)?

        (Enter your answer to at least two decimal places.)

        _______µm

 

        What type of EM wave is this?

        radio

        microwave    

        infrared

        visible light

        ultraviolet

        x-ray

        gamma ray

  

5) The blackbody radiation emitted from a furnace peaks at a       wavelength of 2.5  10^-6 m (0.0000025 m). What is the    temperature inside the furnace?

        _______K

    6) The wavelength of an electromagnetic wave is measured to be 160 m.

        (a) What is the frequency of the wave?

        _______kHz

 

        (b) What type of EM wave is it?

        radio

        microwave    

        infrared

        visible light

        ultraviolet

 

7) A small object is placed to the left of a convex lens and on its     optical axis. The object is 30 cm from the lens, which has a focal length of 46 cm.If the object is moved to a position 40 cm

to the left of the lens, what will the image position be? (A positive value for p, or position, means the image is on the right side of the lens.)

p =_______ cm

 

Describe the nature of this new image. (Select all that apply.)

virtual

real

upright

inverted

enlarged

reduced

on the left side of the lens

on the right side of the lens

 

8) A camera is equipped with a lens with a focal length of 35 cm. When an object 2.4 m (240 cm) away is being photographed, what is the magnification?

________

 

9) List the main types of electromagnetic waves in order of increasing frequency.

 

radio waves, microwaves, infrared, ultraviolet light, visible light, X-rays, gamma rays

 

radio waves, microwaves, infrared, visible light, ultraviolet light, gamma rays, X-rays    

 

radio waves, microwaves, infrared, visible light, ultraviolet light, X-rays, gamma rays

 

radio waves, microwaves, visible light, infrared, ultraviolet light, X-rays, gamma rays

 

microwaves, radio waves, infrared, visible light, ultraviolet light, X-rays, gamma rays

 

 

Give at least one useful application for each type of wave.

 

 

 

 

10) Aircraft equipped with powerful radar units are forbidden from turning them on when on the ground near people. Explain why this is so.

 

 

11) Which type of EM wave does your body emit most strongly?

 

Ultraviolet light.

Visible light.    

Microwaves.

Radio waves.

Infrared.

 

12) Stars emit radiation whose spectrum is very similar to that of a blackbody. Imagine two stars identical in size, each of which is at the same distance from us. One of the stars appears reddish in color, while the other one looks distinctly bluish. Based on this information, what can you say about the relative temperatures of the two stars? Which is the hotter?

 

The relative temperature of a star that is red in color is higher than that of a star that is blue in color.

 

The relative temperature of a star that is red in color is lower than that of a star that is blue in color.    

 

The appearance of a star is independent of its relative temperature; therefore, more information is needed to compare the stars.

There is no difference. Both stars are approximately the same temperature.

 

How do you know?

 

The bluish star emits radiation at a higher frequency and, therefore, a higher energy (temperature).

 

The reddish star emits radiation at a higher frequency and, therefore, a higher energy (temperature).    

 

A star's temperature is not uniform due to its internal and surface temperatures; therefore, knowing only its relative temperature is insufficient.

 

A star's temperature is not uniform due to its internal and surface temperatures; therefore, both stars will have approximately equal average temperatures.

 

13) Describe the greenhouse effect that is occurring in the Earth's atmosphere.

 

 

14) How does the ionosphere affect the range of radio communications?

 

 

 

              


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