Topic 5 - Waves Pt3

Question 1

Why can’t longitudinal waves be polarised?

Answer 1

Because there oscillations are parallel to the direction of wave travel

Question 2

What does it mean if light is unpolarised?

Answer 2

The oscillations are random & not confined to any single plane

Question 3

Explain how receivers are polarised?

Answer 3

They only receive oscillations in 1 direction & must be lined up in the same place to receive the maximum signal

Question 4

What’s stress analyses?

Answer 4

• Different parts of the material reflecting light in different ways
• a polarised filter allows you to see the different levels of stress depending on the colours reflected
• it’s used to detect potential regions of weakness in a material

Question 5

Explain how Polaroid sunglasses are used by fisher men

Answer 5

• unpolarised light from the sun is reflected by the sea
• the reflected light is mainly horizontally polarised
• polarising filter in the glasses cuts our horizontally polarised light
• light reflected from below the surface of the water is mainly vertically polarised & so passes through the polarising filter

Question 6

How is shortsightedness fixed?

Answer 6

Shortsighted = rays focusing before the retina

Fixed with a concave lens (negative power)

Question 7

How is longsightedness fixed?

Answer 7

Rays are focusing behind the retina

Fixed with a convex lens (positive power)

Question 8

What’s absolute refractive index?

Answer 8

It’s how much a wave slows down as it moves from a vacuum in to the medium

Question 9

What’s the midpoint go an oscillation called?

Answer 9

Equilibrium

Question 10

Define oscillation

Answer 10

A repeated movement about a central position

Question 11

What must a body have to be performing a simple harmonic motion?

Answer 11

• must have a restoring force acting upon it
• the magnitude of the force (the acceleration) is proportional to the displacement of the body from a fixed point
• the direction of the force (acceleration) is always towards that fixed point

Question 12

Give 2 examples of a simple harmonic system?

Answer 12

A pendulum

Mass on a spring

Question 13

What’s a radian?

Answer 13

Is the angle subtended at the center of a circle by an arc that’s equal to the length to the radius of the circle

Question 14

How would you convert from degrees to radians?

Answer 14

x pi / 180

Question 15

How would you convert from radians to degrees?

Answer 15

X 180 / pi

Question 16

What’s phase difference?

Answer 16

• It’s the difference in angle between 2 identical waves that are out of step with each other
• when 2 waves have the same periodicity, so same frequency & travel at the same speed if they travel the same distance they’ll keep the same phase difference between
• but if one has to travel longer it comes out of phase

Question 17

What’s path difference?

Answer 17

-it’s the difference (usually in terms of wavelength) between the lengths of 2 paths

Question 18

What’s the phase difference of 2 objects that are oscillating in phase at the same each other (even if they have different amplitudes)?

Answer 18

O or 2 pi radians

Question 19

What’s the phase difference of 2 objects that are exactly out of phase are 1/2 an oscillation apart?

Answer 19

Pi radians