Waves

Question 1

Described transverse wave.

Answer 1

A type of wave in which the particles oscillate perpendicular to the direction the wave travels.

Question 2

Examples of transverse waves.

Answer 2

EM waves, water and s-waves.

Question 3

Describe a longitudinal wave.

Answer 3

A type of wave in which the particles oscillate parallel to the direction of wave travel.

Question 4

Examples of longitudinal waves.

Answer 4

Sound waves and p-waves.

Question 5

What is the wavelength of a wave?

Answer 5

It is the distance between two matching points on neighbouring waves, measured in metres.

Question 6

What is the amplitude of a wave?

Answer 6

Amplitude is the maximum displacement of a point from the centre of oscillation, measured in metres.

Question 7

The larger the amplitude the greater the what of the wave?

Answer 7

The greater the energy of the wave.

Question 8

The period of a wave, T, is what?

Answer 8

The time taken for a point on the wave to move through one complete oscillation.

Question 9

Frequency of a wave is measured in what?

Answer 9

Hertz, Hz.

Question 10

Equation linking time period and frequency of a wave:

Answer 10

f=1/T
Where:
f is frequency in Hz.
T is time period in s.

Question 11

Frequency is a measure of what?

Answer 11

Number of waves that pass a point in 1 second.

Question 12

The wave equation is:

Answer 12

v=fλ
Where:
v is velocity in ms^-1.
f is frequency in Hz.
λ is wavelength in m.

Question 13

Electromagnetic waves are transverse, true or false?

Answer 13

True.

Question 14

True or false, electromagnetic waves travel at different speeds?

Answer 14

False, they all travel at the same speed (speed of light).

Question 15

What speed do electromagnetic waves travel through a vacuum at?

Answer 15

3x10^8ms^-1

Question 16

Typical wavelength for a radiowave is what?

Answer 16

10^3m to a few metres.

Question 17

Typical wavelength for a microwave is what?

Answer 17

10^-2m

Question 18

Typical wavelength for an infrared wave is what?

Answer 18

10^-5m

Question 19

Typical wavelength of visible light is what?

Answer 19

10^-7m

Question 20

Typical wavelength of ultraviolet light is what?

Answer 20

10^-8m

Question 21

Typical wavelength of X-ray radiation is what?

Answer 21

10^-10m

Question 22

Typical wavelength of a gamma ray is what?

Answer 22

10^-12m

Question 23

EM radiation travels by what?

Answer 23

Oscillations in both the electric and magnetic fields.

Question 24

Superposition of waves is what?

Answer 24

Where the waves are both causing the same particle to oscillate causing the amplitudes to be summed.

Question 25

If two waves of the same wavelength and amplitude are perfectly in phase, what can be said about the amplitude of the resultant wave?

Answer 25

It is twice the amplitude of one of the initial waves.

Question 26

When waves cause a resultant wave with a greater amplitude than the initial waves what kind of interference is this?

Answer 26

Constructive interference.

Question 27

When two waves have the same amplitude and wavelength but are perfectly out of phase what can be said about the resultant wave?

Answer 27

There isn’t one. The oscillations of the waves cancel each other perfectly leaving no wave.

Question 28

When two waves cause a resultant wave with less energy than the initial wave what kind of interference is that?

Answer 28

Destructive interference.

Question 29

Waves that are perfectly out of phase have a phase difference of what?

Answer 29

π

Question 30

Calculate what 1 rad is in degrees.

Answer 30

1 rad = 360/2π = 57.3 degrees

Question 31

Calculate what 1 degree is in radians.

Answer 31

1 degree = 2π/360

Question 32

Diffraction is what?

Answer 32

The spreading out of a wave as it passes an obstacle or goes through a gap.

Question 33

In order for diffraction to occur what must be said to be true about the size of obstacle/gap and wavelength?

Answer 33

The obstacle/gap must be a similar size to the wavelength else the diffraction is negligible.

Question 34

What happens to the energy per length of wavefront as a wavefront is being spread out by diffraction?

Answer 34

The energy per length of wavefront decreases.

Question 35

What can be said about the overall energy of the wave as it is diffracted?

Answer 35

The overall energy of the wave remains the same (conservation of energy).

Question 36

What happens to the amplitude of the wavefront during diffraction?

Answer 36

The amplitude decreases.

Question 37

Huygen constructs work by assuming what?

Answer 37

A wavefront can be modelled as a row of oscillating particles that cause wavelets which can be connected to show a wavefront.

Question 38

Diffraction grating equation linking d and N.

Answer 38

d=1/N Where: d is the distance between the slits, m. N is the line density, m^-1.

Question 39

What is the diffraction grating formula?

Answer 39

``` dsinθ=nλ Where: d is the distance between the slits, m. n is the order of the maxima. λis the wavelength, m. ```

Question 40

Define refraction.

Answer 40

The changing of the direction of a wave as it changes medium.

Question 41

What happens if a wave travels from a less dense into a more dense medium?

Answer 41

The wave bends towards the normal.

Question 42

What happens if the wave travels from a more dense into a less dense medium?

Answer 42

The wave bends away from the normal.

Question 43

What is a normal?

Answer 43

The perpendicular to the surface being studied.

Question 44

Snell’s Law using angles:

Answer 44

sini/sinr = n Or n1sinθ1 = n2sinθ2

Question 45

Snell’s Law using velocities:

Answer 45

v1/v2 = n

Question 46

What is the absolute refractive index of a material?

Answer 46

The absolute refractive index for a material is the refractive index of light travelling from a vacuum into a particular substance.

Question 47

Equation for finding the critical angle:

Answer 47

sinc = 1/n Where: c is critical angle. n is the absolute refractive index of the material light is travelling out of.

Question 48

What happens when i

Answer 48

Refraction occurs.

Question 49

What happens when I=θc?

Answer 49

The ray is split part of it is refracted along the very edge of the prism, part is reflected back into the prism.

Question 50

What happens if i>θc?

Answer 50

Total internal reflection occurs.

Question 51

Give everyday uses of total internal reflection (excluding optical fibres).

Answer 51

``` Telescopes (lens). Medical keyhole cameras. Diamonds. Bike reflectors. Cats eyes on the road. ```

Question 52

What are the two types of lenses?

Answer 52

Convex (converging) and concave (diverging).

Question 53

What happens when you look at a close object (within the focal length) through a convex (converging) lens?

Answer 53

The image is: Magnified Upright Virtual

Question 54

What happens if you look at a far object (beyond focal length) through a convex (converging) lens?

Answer 54

The image is: Inverted Diminished Real

Question 55

What happens if you look at an object through a concave (diverging) lens?

Answer 55

The image is: Diminished Upright Virtual

Question 56

What is the centre of a lens known as?

Answer 56

The optical centre.

Question 57

Where is the principle focus on a convex (converging) lens?

Answer 57

Where all rays converge (cross).

Question 58

Where is the principle focus on a concave (diverging) lens?

Answer 58

When the diverging rays are traced backwards and the they all converge, this is where the principle focus is.

Question 59

What is a node on a stationary wave?

Answer 59

A point of minimum displacement.

Question 60

What is an antinode on a stationary wave?

Answer 60

A point of maximum displacement.

Question 61

What does the first harmonic look like on a string?

Answer 61

The first harmonic on a string is when the wave is stationary and there is a node at each end with one antinode in the middle.

Question 62

What can be said about the wavelength of the wave if the first harmonic is produced in a string?

Answer 62

The wavelength will be 2x the length of the string.

Question 63

The fundamental frequency of a wave is the frequency when...

Answer 63

...the first harmonic is produced as a standing wave.

Question 64

Wave speed in a string depends on what?

Answer 64

Length, tension and material.

Question 65

Stationary waves in strings always start and end in what?

Answer 65

Nodes.

Question 66

What can be said about the wavelength of the second harmonic in a string?

Answer 66

The wavelength is equal to the length of the string.

Question 67

What can be said about the wavelength of the third harmonic in a string?

Answer 67

It is equal to 2/3 length of the string.

Question 68

What can be said about the frequencies of the 2 and 3rd harmonics for a stationary wave in a string?

Answer 68

The frequency of the second is 2x the fundamental frequency. | The frequency of the third is 3x the fundamental frequency.

Question 69

What can be said is at the start and end of a stationary wave in a closed pipe?

Answer 69

There is always an antinode at the open end (start) and a node at the closed end (end).

Question 70

Can we get all harmonics in a closed pipe?

Answer 70

No we can only get odd harmonics, so 1st, 3rd, 5th etc.

Question 71

Can we get all harmonics with an open pipe?

Answer 71

No we can only get the even harmonics.

Question 72

What can be said about the start and end of a stationary wave in an open pipe?

Answer 72

The wave starts and ends with both antinodes.