P2: Waves 1

Question 1

What is a wave

Answer 1

• A wave transfers energy from one place to another

WITHOUT

• transferring matter

Question 2

How is a wave created

Answer 2

• Something vibrates
• Collection of particles or an electromagnetic field

Question 3

What is a transverse wave

Answer 3

• Wave with vibrations that a perpendicular to the direction of travel
• Have peaks and troughs

example:

• Water waves
• Light waves
• Mexican wave

Question 4

What is a longitudinal wave

Answer 4

• Vibrations are parallel to the direction of travel
• Compressions and rarefactions

example:

• Sound

Question 5

What is frequency ?

Answer 5

• The number of vibrations per second
• Unit: Hertz, Hz

Question 6

What is the definition of time period

Answer 6

• Time for one wave to pass a point
• Unit: seconds
• 1/frequency

Question 7

What is the definition of amplitude?

Answer 7

• Maximum displacement of a vibration from its resting position
• from middle line to peak/trough

Question 8

What is wavelength

Answer 8

• distance from a point on a wave to the same point on the next wave
• unit: Meters

Question 9

What are peak/troughs

Answer 9

• Trough=lowest point
• Peak = highest point

Question 10

What is wave speed

Answer 10

• The speed at which energy is transferred through a medium

Question 11

How do you measure the speed of sound in air

Answer 11

• Person 1 stand far away from Person 2
• Measure the distance using a meter ruler
• Person 1 makes an obvious noise (loud and visible)
• Person 2 times from when they see the noise to when they hear it
• Speed = distance/time

Question 12

What is the equation for a wave length

Answer 12

Wave speed = frequency x wavelength

Question 13

How can you measure the speed of ripples on the surface of water

Answer 13

• Using a ripple tank
• Measure distance across 10 waves
  
  • Using a ruler
• Divide by 10 to find 1 wavelength
• Read the frequency of the signal generator
• Speed = frequency x wavelength

Question 14

How would you determine the speed of waves using a string

Answer 14

• Stretch a string over a pulley
  
  • Using a mass
• Use a frequency generator to generate a wave in the string
  - (bump up bump down)
• Measure the wavelength
  - Using a ruler
• Measure the frequency
  
  • from the frequency generator
• Wavespeed = wavelength x frequency

Question 15

How can you vary wave speed?

Answer 15

• Vary the frequency using the frequency generator
• Change the tension of the string by changing the masses

Question 16

What is a diffuse reflection

Answer 16

• Bumpy surface
• rays of light do not remain parallel
• No image

Question 17

What is a specular relfection

Answer 17

• Smooth surface
• Rays of incident light are reflected and stay parallel
• Can produce image

Question 18

What is the law of reflection

Answer 18

The angle of incidence = angle of reflection

• Incidence -> going in
• Reflection -> going out
• Normal -> @ 90 to the reflective surface

Question 19

What does a ray diagram look like

Answer 19

• Object reflected in mirror
• Light reaches eyes
• Line that just reached eyes can be continued in the other direction to create the image
• Image and object same distance away from normal

Question 20

What is a virtual image vs real image

Answer 20

• Rays of light appear to come from a virtual image, rather than pass through it
• Cannot be projected
• In a real image rays of light actually pass though the image
• Can be projected

Question 21

What is refraction and why does it happen

Answer 21

• Change in speed of a wave
• Reaches a boundary between 2 materials with DIFFERENT OPTICAL DENSITIES
• When an object goes into a more dense object it slows down
• If a ray enter the object at an angle it turns towards the normal

Question 22

What happens to frequency and wavelength (refraction)

Answer 22

• Frequency doesn’t change
  
  • Source of wave doesn’t change
• wave speeds up as its gone into a less dense object wavelength increase
  
  • wavespeed (^) = frequency (constant) x wavelength (^)

(less dense, more speed, bigger wavelength, away from normal)

Question 23

Explain what a wavefront diagram shows

Answer 23

• Distance between lines = wavelength

Question 24

What does the refraction of light lead to

Answer 24

At water/air boundary
- Objects appear closer to the surface than they are

• Why straws look broken in water

Question 25

What happens to parallel rays of ligjt when they enter a CONVEX lense

Answer 25

- Convex = () - Parallel rays hit and converge (meet) at a point known as the focal point - Distance between this point and the centre of the lens is called the focal length

Question 26

Object through Convex lens look like

Answer 26

- Depends on where the object is and the focal length Options are: - real vs virtual - inverted vs upright - magnified or diminished If in doubt draw it out

Question 27

Convex lens: Object = > 2 focal lengths

Answer 27

- Real - Inverted - Dimished

Question 28

Convex lens: Object = 1Focal length - 2 focal lengths

Answer 28

- Real - Inverted - Magnified

Question 29

Convex lens: Object = focal length

Answer 29

- NO IMAGE

Question 30

Convex lens: Object = < 1 focal length

Answer 30

- Virtual - Upright - Magnified

Question 31

How do you draw a lens diagram

Answer 31

1. Draw a ray from the top of the object horizontal to the lens then through the focal point 2. Draw ray from top of image through the centre of the lens Where they cross is the image

Question 32

What happnes to parallel rays of light when they enter a cooncave lense

Answer 32

- Concave = )( - Parallel rays of light diverge away from the lens - Focal point is on the same side of the lens as the object

Question 33

What do objects viewed through a concave lens look like

Answer 33

- Diminished - Right way up - Virtual

Question 34

How do you calculate magnification

Answer 34

Magnification = image height / object height - Image and object must be measured in the same unit (probably cm)

Question 35

What happens to white light when its shone through a prism

Answer 35

- Colours separate - spectrum of light seen - called dispersion - different colours have different wavelengths so refract dfferent amounts

Question 36

Why do opaque object apear as they do

Answer 36

- Coloured object reflect wavelengths of light that they appear - Absorb the rest - White reflect everything - Black absorbs everything

Question 37

What are transparent and translucent objects

Answer 37

- Both transmit light that is shone on them - Translucent only partially

Question 38

What is a filter

Answer 38

- A filter only allows light of the wavelength of its colour to pass through (transmitted) - Other wave lengths transmitted

Question 39

What happens to the colour of an object when viewd through a coloured object

Answer 39

- If the filter allows the wavelengths of the object colour through , it will look that colour - If it doesn't the object will look black

Question 40

When a wave arrieves at a change of substance what could happen

Answer 40

- Absorbed - Transmitted - reflected - Refracted

Question 41

How do you measure the path of light through a glass block

Answer 41

- Place the glass block on a piece of paper and draw around it - Draw a normal to the block and align the ray of light from the ray box with the meeting point between the normal and the surface of the block - Draw the reflected and refracted ray then remove the block and join up the lines - Use a protractor to measure the angle of incidence, reflection and refraction - Repeat and change the angle of incidence each time