Waves and Optics

Define amplitude and give its unit of measurement.

The maximum distance particles move from rest. Measured in m/cm

Define wavelength and give its unit of measurement.

The distance between two consecutive identical points in a wave cycle. Measured in m/cm

Define frequency and give its unit of measurement.

The number of wave cycles per second. Measured in Hz/Hertz

Define time period and give its unit of measurement.

The time taken for one wave cycle. Measured in seconds.

What is a transverse wave? Give some examples.

Waves in which particles oscillate perpendicular to the direction of energy transfer, e.g. light waves, gamma waves, radio waves

What is a longitudinal wave? Give an example.

Waves in which particles oscillate parallel to the direction of energy transfer, e.g. sound waves

What is the order of the EM spectrum from shortest to longest wavelength?

Gamma rays, X-rays, Ultraviolet, visible light, infrared, microwaves, radio waves

What is the equation for time period? Rearrange it to give another form.

• T = 1/f

• f = 1/T

What is the formula for wave speed? Rearrange it to give other forms.

• v = f * lambda

• Lambda = v / f

• f = v / lambda

How do these things change when light waves go from a less optically dense medium to a more optically dense medium?:

• wave direction relative to normal

• Wave speed

• Frequency

• Wavelength

• towards the normal

• Slows down

• No change

• Decreases

How do these things change when light waves go from a more optically dense medium to a less optically dense medium?:

• wave direction relative to normal

• Wave speed

• Frequency

• Wavelength

• away from normal

• Gets faster

• No change

• Increases

Define the angle of incidence and the angle of refraction.

• the angle of incidence is the angle between the incident light ray and the normal

• The angle of refraction is the angle between the refracted light ray and the normal

When light waves meet a boundary, what three things can occur?

• reflected off the boundary

• Absorbed by the boundary

• Transmitted (passes straight through)

TIR is when _____ waves are _______ inside a ______ medium.

light, trapped, denser

What are the two conditions that apply to TIR?

• the light rays must be “attempting” to travel from an optically denser medium to a less dense medium.

• The angle of incidence must be greater than a certain minimum angle, called the critical angle.

What is the critical angle for glass-air?

42 degrees.

If the angle of incidence is less than the critical angle, what happens?

most light leaves the glass, refracting away from the normal

If the angle of incidence is greater than or equal to the critical angle, what happens?

TIR occurs - light rays reflect back into glass.

Name the uses of TIR.

• optical fibres - these are used in communications (e.g. internet / phone lines) and in medical environments (e.g. endoscopes and colonoscopes)

• Right-angled prisms - used in cats’ eyes (reflectors on roads to help drivers see at night), bike reflectors, binoculars, and periscopes.

What is a lens?

A piece of glass, shaped in a particular way so it refracts light rays to the same point.

What do these lenses look like:

• convex

• Concave

• convex is thick in the middle and thin on ends.

• Concave is thick on the ends and thin in the middle

What are some other names for convex and concave lenses?

Convex lenses are known as converging lenses (they make light rays meet at the same point), but concave lenses are known as diverging lenses (they make light rays go away from each other).

What is the focal length?

The length from the optical centre to the principle focus.

What is the focal point?

the key spot where parallel light rays converge (meet) for a convex lens or appear to diverge from for a concave lens

When are real images formed? What orientation are real images usually?

• formed when light rays meet

• Usually upside-down

When are virtual images formed? What is the orientation of these usually?

• formed when construction lines cross over

• Usually upright