RP: Infrared Radiation

What is Required Practical 10?

Investigate how the absorption or emission of infrared radiation depends on the nature of a surface.

Which surfaces are generally the best absorbers of infrared radiation?

Matt black surfaces.

Which surfaces are generally the best emitters of infrared radiation?

Matt black surfaces.

Which surfaces are generally poor absorbers of infrared radiation?

Shiny, light-coloured surfaces.

Which surfaces are generally poor emitters of infrared radiation?

Shiny, reflective surfaces.

How can infrared absorption be investigated?

Expose different surfaces to the same infrared source and compare their temperature increases over the same time.

What is the independent variable when investigating infrared absorption?

The type or nature of the surface.

What is the dependent variable when investigating infrared absorption?

The temperature increase over a fixed time.

What control variables are needed in an infrared absorption investigation?

Distance from the source, exposure time, initial temperature and the size and material of the objects.

Why should the objects start at the same temperature?

To ensure a fair comparison of temperature changes.

Why should the distance from the infrared source be kept constant?

To ensure each surface receives comparable incident radiation.

How can infrared emission be investigated?

Fill identical containers with hot water, give them different surface finishes and compare their cooling rates.

What is the independent variable when investigating infrared emission?

The surface finish of the container.

What is the dependent variable when investigating infrared emission?

The rate of cooling or temperature decrease.

What control variables are needed when investigating infrared emission?

Initial temperature, water volume, container dimensions, material and surroundings.

Why should identical containers be used?

To ensure differences in cooling are mainly due to surface finish.

Why should temperature readings be taken at regular intervals?

To compare temperature changes over time.

Why should repeated readings be taken?

To identify anomalies and improve reliability.

What graph can be drawn for an infrared emission investigation?

Temperature against time for each surface.

What would a steeper downward temperature–time graph indicate?

A faster rate of cooling.

Why must other methods of energy transfer be considered?

Conduction and convection may also affect temperature changes.

What is the expected conclusion of Required Practical 10?

Matt black surfaces are generally better absorbers and emitters of infrared radiation than shiny surfaces.