Required Practicals - Infrared

Question 1

What do hot surfaces emit?

Answer 1

Infrared radiation

Light

Question 2

Can the human eye see infrared radiation?

Answer 2

No

Question 3

What are we investigating in the practical?

Answer 3

How much infrared is emitted or absorbed by different surfaces.

Question 4

What is a Leslie’s Cube?

Answer 4

A cube with 4 different materials on 4 sides which emit or absorb different levels of infrared radiation.

Question 5

What can we use a Leslie’s Cube for?

Answer 5

To see how much infrared is emitted from different surfaces.

Question 6

Which surfaces are there on a Leslie’s Cube?

Answer 6

A shiny metallic side

A white side

A shiny black side

A matte black side.

Question 7

What do we do with the Leslie’s Cube?

Answer 7

First, fill it with hot water.

Point an infrared detector at each of the four surfaces and record the amount of infrared emitted.

Question 8

What do we keep the same when measuring different sides of a Leslie’s Cube?

Answer 8

The distance between the cube and the infrared detector.

Question 9

Why do we keep the distance between the detector and the cube the same?

Answer 9

It makes the measurements repeatable.

Question 10

How does infrared emission change with different sides of a Leslie’s Cube? (go from most to least emitting)

Answer 10

Matte black - most emitting

Shiny black

White

Shiny metallic - least emitting

Question 11

What can we use if we do not have an infrared detector?

Answer 11

Use a thermometer with the bulb painted black.

Question 12

What is the problem with using a thermometer as opposed to a infrared detector to measure emission rates?

Answer 12

The resolution of the thermometer is less than the infrared detector.

Question 13

What is resolution of a device?

Answer 13

The smallest change that can be detected by it.

Question 14

How do we measure the absorbance by different surfaces?

Answer 14

Have an infrared heater with metal plates on two sides.

One plate is painted shiny metallic whereas the other is painted matte black.

We have vaseline attached to a drawing pin on each side.

Switch on the heater and start timing.

The temperature of the metal plates increases as they absorb infrared.

Record the time taken for vaseline to melt and drawing pins to fall off.

Question 15

What results do we find for the absorbance practical?

Answer 15

The drawing pin falls off first on the matte black plate first.

Question 16

Why does the drawing pin fall off the matte black plate first?

Answer 16

Matte black surfaces absorb more infrared than shiny metallic surfaces.

Question 17

What results can we gather from the practical?

Answer 17

Matte black surfaces are much better at emitting and absorbing infrared than shiny metallic surfaces.

Question 18

What can we say about infrared on shiny metallic surfaces?

Answer 18

It tends to be reflected by them instead of being absorbed.