physics: topic 6 = waves

What are waves?

Transfer of energy from one place to another

What do particles do in waves?

The oscillate but don’t change overall position

What are longitudinal waves?

• energy transfer parallel to movement

• E.g. sound or shock

What are transverse waves?

• energy transfer perpendicular to movement

• E.g. light or water

What is apmplitude?

The maximum displacement from the starting position

What is frequency

Number of wavelengths passing a point per second

What is wavelength ?

The distance between the same point in two waves (e.g peak to peak)

What is the peak?

The point of the wave with the maximum positive displacement (up)

What is the trough?

The point of the wave with the maximum negative displacement (down)

What is compression?

Where the wave fronts are closest to one another

Rarefaction

Where the wave fronts are furthest away from each other

What does amplitude affect?

• volume

• Big amplitude = higher volume

What does frequency affect?

• Measures in Hz

• pitch in sound

• Colour in light

• High frequency = high pitch + blue

• Low frequency = low pitch + red

What is the period of a wave?

• time taken to produce one wave

• Shorter period = higher frequency

• Frequency and period are inversely proportional

Equation for period?

Period = 1/frequency

Wavelength?

• frequency is inversely proportional to wave length

• Wave speed = frequency x wavelength

What kind of surface do objects that reflect light have?

Smooth, shiny surfaces

What is true about an image you see in a mirror?

• virtual (cannot be touched or projected onto a screen)

• Upright (right way up)

• Laterally inverted ( your left appears to be your right)

What is the law of reflection?

The angle of incidence for a plane mirror must be equal to the angle of reflection

What does refraction occur?

Because light can change direction when it is transmitted into a different medium (material)

• happens with all waves

When does refraction occur?

• only when the angle of incidence is not 0 degrees, not coming in at 90 degrees

Relationship between angle of incidence + angle of refraction

As one increases so does the other but not same size

Rules for refraction in light?

• low density medium to high density medium (e.g. air to glass):

  • light slows down

  • Smaller angle of refraction than angle of incidence

• High to low density is reverse

What is the equipment needed for the ripple tank experiment?

• ripple tank

• Stop clock

• Ruler

• Camera (sometimes)

What is the method for the ripple tank experiment?

• set up ripple tank as shown in diagram with about 5 cm of water

• Switch on lamp ans motor, adjust until low frequency waves can clearly be seen

• Measure length of screen and then divide this by the number of waves seen to record wave length

  • may need to to use a slo mo video or take a picture

  • Count the number of waves passing a particular point per 10 seconds, divide by 10 to find the frequency

  • Calculate the speed of waves using wave speed = frequency x wavelength

What equipment is needed for the string experiment?

• metre ruler

• Two clamp stands

• Vibration generator

• Power supply

• Wires

What is the process for the string experiment?

• attach string to vibration generator and use a 200g hanging mass and pulley to pull string taut as shown, place wooden bridge under string near pulley

• Switch on vibration generator and adjust the wooden bridge until stationary waves can be seen

• Measure the lengths of as many half wavelengths as possible divide by the number of wavelengths. Double this too find a full wavelength

• Frequency is frequency of power supply

• Calculate speed using speed = frequency x wavelength

What are the variables for the refraction practical?

• independent: angle of incidence

• Dependent: angle of refraction

• Control : sam Perspex block (same material) and same protractor

Refraction practicle method?

• place ruler horizontal along the middle of a plain piece of paper and draw a straight line

• Use a protractor to draw a dotted line 90 to the straight line (this is the normal line)

• Place longest side of Perspex block against the first line

• Use the ray box to shine a ray to the point at which the normal line meets the block

• Mark both this line with an x and the refraction line on the other side with an x as close to the box as possible

• draw a line bewteen both of the x’s and the point where the normal line meets the horizontal line, measure the anglea between both these lines and the normal line, the angle between the normal and incident ray is the angle of incidence and the angle between the rrfracted ray and the normal line is the angle od refraction

• repeat with tye ray box at other angles