General overview (light and the electromagnetic spectrum)

What is total internal reflection?

Light is completely reflected back at a boundary between two mediums. It occurs when light meets a less dense medium at an angle of incidence larger than the critical angle

What is the law of reflection?

Angle of incidence=angle of reflection

What is a critical angle?

The angle of incidence in the denser medium which causes the angle of refraction to be 90 degrees

What is speculation reflection?

Rays are reflected from a smooth surface in a single direction

What is diffuse reflection?

Reflection from a rough surface which causes scattering

Draw a labelled diagram showing refraction of a ray from air into glass

Labels should include: normal (dotted line), incident ray (first line), refracted ray (second line), angle of incidence (first angle), angle of reflection (second angle)

Draw a labelled diagram to show reflection against a plane mirror

Labels should include: incident ray, reflected ray, plane mirror, normal, angle of incidence, angle of reflection

Draw diagrams to show total internal reflection from water to air

Why do some objects appear certain colours?

Opaque objects only reflect a specific wavelength, causing the object to appear that colour - all other wavelengths are absorbed

How do filters work?

Only a certain colour is transmitted through the filter - all other colours are absorbed

What is the focal length of a lens?

Distance between the lens and the focal point

What is a focal point?

The point where all horizontal rays meet after passing through the lens

How is the focal length of a lens related to its power?

Power is the inverse of the focal length. The shorter the focal length, the greater the power

What is a concave lens?

Also called a diverging lens, it is thinner at the centre than the edges (hourglass-like)

How do concave lenses refract light?

Parallel rays are caused to diverge. They separate, but come to form a principle focus on the other side of the lens

What type of image does a concave lens produce?

A virtual image only

What is a convex lens?

Also called a converging lens, it is thicker in the middle than at the edges

How do convex lenses refract light?

Parallel light rays converge

What type of image does a convex lens produce?

Can produce both real and virtual images

What type of waves are electromagnetic waves?

Transverse

What do electromagnetic waves transfer?

Energy only

What are the main groups in the magnetic spectrum?

Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays

What type of spectrum is the electromagnetic spectrum?

Continuous (each group goes into the next)

What trends are there in the electromagnetic spectrum?

As wavelength increases, frequency decreases

Danger also increases (gamma rays can cause cancer while radio waves aren’t dangerous at all)

What can happen when radiation hits an object?

It can be transmitted, reflected or absorbed

What do all objects emit and absorb?

Infrared radiation

How does the quantity of infracted radiation increase?

If temperature increases

What happens to the type of radiation emitted by an object as temperature increases?

Wavelength decreases

What is required for a body to be at a constant temperature?

It should emit radiation at the same rate it absorbs it on average

What happens to the body if the average power it radiates is less than the power it absorbs?

The temperature of the body decreases

What happens to the body if the average power it radiates is more than the power it absorbs?

The body increases in temperature

What factors control the temperature of the earth?

The rate of absorption and emission of radiation, and the amount of reflection of radiation into space

What happens to how dangerous an electromagnetic wave is as frequency increases?

It increases

What is the danger of microwaves?

Internal heating of body cells

What is the danger of infrared waves?

Skin burns

What are the dangers of visible light waves?

Blindness

What are the dangers of ultraviolet waves?

Damage to surface cells and eyes, which can lead to skin cancer

What are the dangers of x-rays and gamma waves?

Mutation to cells and cell damage

What are radio waves used for?

Broadcasting, communications, satellite transmissions

What are infrared waves used for?

Thermal imaging, optical fibres, security systems

What is visible light used for?

Photography, vision, illumination

What are gamma rays used for?

Sterilising food, detection and treatment of cancer, sterilising medical equipment

How are radio waves and electrical circuits linked?

They can be produced by oscillations in electrical circuits, and they can induce oscillations in electrical circuits

What can changes in atoms and nuclei do?

Generate radiations over wide frequency ranges

What can cause a change in atoms and nuclei?

Absorption of a range of radiations