Topic 4 - Oscillations and waves

Question 1

What are examples of oscillations?

Answer 1

1. Tides of the ocean
2. The movement of our legs when we walk
3. A heart beating
4. Clock mechanisms
5. Atoms vibrating
6. Machinery and engines
7. A guitar string played
8. Eardrums
9. Radio waves and microwaves

Question 2

What is the displacement of an oscillator (x)?

Answer 2

The distance in a specified direction from its equilibrium position

Question 3

What is amplitude (x₀)?

Answer 3

The maximum displacement, the distance from the equilibrium position to the furthest point of travel

Question 4

What is period (T)?

Answer 4

The time it takes for one complete oscillation

Question 5

What is frequency (ƒ)?

Answer 5

The number of oscillations in unit time (second)

Question 6

What is the relationship between frequency and period?

Answer 6

Question 7

What is phase difference?

Answer 7

The angle (radians) between two similar oscillations

Question 8

What is angular frequency (angular speed)(ω)?

Answer 8

Unit: rads^–1

Question 9

What is simple harmonic motion?

Answer 9

An oscillation in which the acceleration (a) of a body is proportional to its displacement (x) from its equilibrium position and in the opposite direction

Question 10

What is the interchange between kinetic energy and potential energy during SHM?

Answer 10

All mechanical oscillations involve a continual interchange between kinetic energy and some form of potential energy

Question 11

What is the kinetic energy, potential energy, and total energy of SHM?

Answer 11

Question 12

What is damping?

Answer 12

The dissipation of energy of an oscillator due to resistive forces

Question 13

What are the types of damping?

Answer 13

1. Light damping
2. Heavy damping
3. Critical damping

Question 14

What is natural frequency of vibration?

Answer 14

When something is disturbed and then left to osillate without further interference, it is said to oscillate at its natural frequency of vibration

Question 15

What is forced oscillation?

Answer 15

Occurs when an external oscillating force acts on another system tending to make it oscillate at a frequency which may be different from its natural frequency

Question 16

What is resonance?

Answer 16

The increase in amplitude and energy of an oscillation that occurs when an external oscillating force has the same frequency as the natural frequency of the system

Question 17

What are examples of unwanted resonance?

Answer 17

1. Parts of engines and machinery vibrate
2. Earthquakes
3. Strong winds can cause resonance in bridges

Question 18

What are examples of useful resonance?

Answer 18

1. Radios and TVs are tuned by changing the frequency to mach the transmitted signal
2. Quartz crystals can be made to resonate and it’s useful in driving accurate timing
3. Magnetic resonance imaging (MRI)

Question 19

What are continuous progressive (travelling) waves?

Answer 19

Waves which transfer energy away from a source

Question 20

What is a wave pulse?

Answer 20

A wave formed from a disturbance of single oscillation (not continuous)

Question 21

Do progressive (travelling) waves transfer energy?

Answer 21

Yes.

Question 22

Describe transverse waves?

Answer 22

• Parts of the medium are not all moving in phase
• Each part of the medium oscillates perpendicularly to the direction in which the wave is transferring energy
• They have troughs and crests
  e. g. light and other EM waves and water waves

Question 23

Describe longitudinal waves

Answer 23

• Each part of the medium oscillates parallel to the direction in which the wave is transferring energy
• Have compressions and rarefactions
• The medium in which the wave transfers energy does not undergo net translational motion away from the source
  e. g. sound and eartquakes

Question 24

What is a wavefront?

Answer 24

A line joining adjacent points moving in phase in a wave

Question 25

How can wavelength be determined from wavefronts?

Answer 25

The distance between adjacent wavefronts is the wavelength

Question 26

What is a ray?

Answer 26

A line pointing in the direciton in which the wave is transferring energy

Question 27

What is the intensity (I) of a wave?

Answer 27

The wave power passing through unit area Unit: Wm^–2

Question 28

What is wavelength (λ)?

Answer 28

The shortest distance between two points moving in phase

Question 29

What is wave speed?

Answer 29

The distance travelled by a wave (wavefront) in unit time

Question 30

What is the relationship between wave speed, wavelength, and frequency?

Answer 30

v = ƒλ

Question 31

Do all electromagnetic waves travel with the same speed in free space?

Answer 31

Yes

Question 32

What happens to waves when they are reflected on a surface?

Answer 32

The angle of incidence (i) is equal to the angle of reflection (r)

Question 33

What happens to waves when they travel into a different medium?

Answer 33

Their speed changes

Question 34

What is refractive index (n)?

Answer 34

The ratio of the speeds of the wave in the two media and also of the angles of indicendence and refraction

Question 35

What is Snell's law?

Answer 35

Question 36

What is diffraction?

Answer 36

The effect when waves pass through gaps (apertures) or pass around obstacles in their path and spread or bend around them

Question 37

Describe the diffraction around different gaps and obstacles

Answer 37

Question 38

What are examples of diffraction?

Answer 38

1. Sound is diffracted around corners, buildings, doors, and furniture 2. Light is diffracted in the eye 3. Radio waves need to diffract around buildings and various obstacles to reach the receivers 4. The diffraction of X-rays is used to study the arrangement of atoms

Question 39

What is the principle of superposition?

Answer 39

At any moment the overall displacement at any point will be the vector sum of all the individual wave displacements

Question 40

What is constructive interference?

Answer 40

- Occurs when coherent waves arrive at a point in phase - Occurs when the path difference is equal to a whole number of wavelengths: path difference = nλ

Question 41

What is destructive interference?

Answer 41

- Occurs when coherent waves arrive at a point exactly out of phase - Occurs when the path difference equals to an odd number of half wavelengths: path difference = (n + 1/2)λ