Physics 6.4.1

Question 1

What is ‘Black Body Radiation’?

Answer 1

Black Body Radiation is the name given to the Thermal Radiation Emitted by all Bodies (Objects).

Question 2

The ___ the Object, the More Infrared Radiation it Radiates in a Given Time.

Answer 2

Hotter.

Question 3

What is a ‘Perfect Black Body’?

Answer 3

An Object that Absorbs all of the Radiation Incident on it, & Does not Reflect or Transmit any Radiation.

Question 4

Since a Good Absorber is Also a Good Emitter, a Perfect Black Body would Also be the…

Answer 4

Best Possible Emitter too.

Question 5

Why is an Object which Perfectly Absorbs all Radiation Always Black?

Answer 5

Because the Colour Black is what is Seen when All Colours from the Visible Light Spectrum are Absorbed.

Question 6

All Objects Emit…

Answer 6

Thermal Energy, in the Form of Electromagnetic Waves (Infrared Radiation).

Question 7

The Hotter the Object, the More ___ ___ it will Emit, in the Form of…

Answer 7

Thermal Energy, Electromagnetic Waves (Infrared Radiation).

Question 8

The Hotter the Object, the More Thermal Energy it Emits, in the Form of Electromagnetic Waves (Infrared Radiation). The Hotter the Object, the ___ the Wavelength of the Infrared Radiation. Why is this?

Answer 8

Shorter. This is Because the Shorter the Wavelength, the Higher the Energy it has. (In this case, Thermal Energy).

Question 9

Why do Extremely Hot Objects (eg Heating Up a Metal Crowbar in Fire) Produce Visible Light (Glow)?

Answer 9

Because the Hotter the Object, the More Thermal Energy it Emits, as Electromagnetic Waves. Normally, the Thermal Energy is Emitted in the Form of EM Waves of Infrared Radiation. But, Since here, there is Lots of Thermal Energy, the Wavelength of the EM Waves is Shorter (Shorter Wavelength = Higher Energy), and, Visible Light EM Waves Have Shorter Wavelengths than Infrared EM Waves.

They Produce Visible Light, because they have High Thermal Energy, so the EM Waves have Shorter Wavelengths. So, since Visible Light EM Waves have Shorter Wavelengths (Higher Energy) than Infrared EM Waves, Visible Light is Produced.

Question 10

At Very High Temperatures, the ___ & the ___ of the Radiation Emitted by the Object Increase & Decrease Respectively.

Answer 10

Intensity, Wavelength.

Question 11

The Perfect Black Body Object Absorbs all Radiation Incident on it. So, no Light is ___ or ___. This is Because it is all ___.

Answer 11

Reflected, Transmitted, Absorbed.

Question 12

The Perfect Black Body is Also the…

Answer 12

Best Possible Emitter of Radiation.

Question 13

The Perfect Black Body is the Perfect Absorber of Radiation. It is Also the Best Possible Emitter of Radiation. Why is this?

Answer 13

This is Because an Object that Absorbs Radiation well will Also Emit Radiation well.

Question 14

What Will Happen if an Object is Warmer than its Surroundings?

Answer 14

If an Object is Warmer than its Surroundings, it Will Emit More (Infrared) Radiation than it Absorbs, & its Temperature Will Decrease. (Loses Thermal Energy to Surroundings).

Question 15

What Will Happen if an Object is Cooler than its Surroundings?

Answer 15

If an Object is Cooler than its Surroundings, it Will Absorb More (Infrared) Radiation than it Emits, & its Temperature Will Increase. (Gains Thermal Energy from Surroundings).

Question 16

What Will Happen if an Object is at a Constant Temperature?

Answer 16

If an Object is at a Constant Temperature, it is Absorbing (Infrared) Radiation at the Same Rate at which it is Emitting (Infrared) Radiation. (Temperature of Object Remains Constant).

Question 17

What are the Only Ways that the Earth Can Gain / Lose Energy? (2)

Answer 17

-Absorbing Radiation.

-Emitting Radiation.

Question 18

The Sun Emits ___ Wavelength Radiation, eg Visible Light & Ultra Violet. This Radiation Travels to the ___. Some of this Radiation is Simply ___, eg by Clouds. The Remaining Radiation, however, Can then be ___ by the Surface of the Earth. What does this Cause? What does the Earth now do? What Happens to Some of this Infrared Radiation?

Answer 18

Short (High Energy EM Waves), Earth, Reflected, Absorbed.

This Causes the Temperature of the Earth to Increase.

Now, the Earth Emits Thermal Energy back into Space, as Infrared Radiation EM Waves.

However, Some of the Thermal Energy of the Infrared is Trapped by Greenhouse Gasses in the Atmosphere, eg Carbon Dioxide. This Causes Global Warming, & CC.

Question 19

Why are Cloudy Nights Usually Warmer than Cloudless Nights?

Answer 19

Because the Clouds Can Reflect the Infrared Radiation EM Waves (Carrying Thermal Energy) that are Being Emitted by the Earth back into Space, back, so then they Remain on Earth, Within Our Atmosphere. So Therefore, the Earth Remains Warmer on Cloudy Nights.