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Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

Why does radio reception improve slightly during the night ? 

  1. The outside noise is reduced very much at night.

  2. Unlike the daytime, only a few radio stations broadcast during the night.

  3. Sunlight affects radio broadcasts to some extent during the day.

  4. The magnetic field of the earth acts with reduced intensity during the night, thereby reducing its impact on broadcasts.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Answer is C.

The D region is the lowest of the regions within the ionosphere that affects radio communications signals to any degree. It is present at altitudes between about 60 and 90 kilometers and the radiation within it is only present during the day to an extent that affects radio waves noticeably. It is sustained by the radiation from the Sun and levels of ionization fall rapidly at dusk when the source of radiation is removed. It mainly has the affect of absorbing or attenuating radio communications signals particularly in the LF and MF portions of the radio spectrum, its affect reducing with frequency. At night it has little effect on most radio communications signals although there is still a sufficient level of ionization for it to refract VLF signals.
Hence, radio reception improve slightly during the night because, sunlight affects radio broadcasts to some extent during the day.

Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

Infrared radiation was discovered in $1800$ by.

  1. William Wollaston

  2. William Herschel

  3. Wilhelm Roentgen

  4. Thomas Young
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Infrared radiation was discovered in $1800$ by $William Herschel$.

They discovered $\longrightarrow $ When sunlight went through various color filters; it produces different amount of heat. He hypothesized that colors could have different temperatures. He then passed light through glass prism, creating a color spectrum and analysing each color's temperature. He used three special thermometers.
For each color, one was placed within its bounds while the other two were outside as controls. The thermometer in the color had higher temperature than the others, and he found that each color going from violet to red was warmer than the last. He then placed a thermometer next to red light, where no color from spectrum were visible. He noticed that area had even higher temperature than color sections. He demonstrated that this visible type of light refracted and reflected the same way sunlight did.This light came to be known as infrared radiation.

Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

State whether true or false :

Ultraviolet rays are used to take photographs in darkness.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Wrong

Infrared is used in dark for photography. All body emit infrared radiation every time.
Since infrared radiation is invisible, photography in total darkness can be readily carried out if infrared film is used and the light source is covered with a light-absorbing but infrared-transmitting filter.

Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

 Which one of waves tans our skin and causes some substances to become fluorescent?

  1. infrared waves.

  2. ultraviolet waves.

  3. gamma rays.

  4. infrared and ultraviolet waves both.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ultraviolet rays (or waves) tan our skin and cause some substances to become fluoroseun sun is important source of ultraviolet light. Sun rays reach our skin and burns the upper layer of skin, causing sunburns prolonged doses of UV radiation can induce skin cancer in human beings.

Ozone layer is protecting us from UV rays but the problem is that Ozone layer is also depleting because of excessive use of CFC's.