Past papers- 3. waves Flashcards
short‑sightedness and long-sightedness which lens is used and why
diverging lens in front of eye lens
rays meeting on the retina
converging lens reduces focal length of eye OR converging lens brings focal point forward OR without lens, rays converge behind back of eye
(so that) rays converge / focus on back of eye / retina
compression and rarefaction
(region where) particles are close(r) together (than normal) OR (region where) there is a great(er) pressure (than normal)
(region where) particles are further / far apart (than normal) OR (region where) there is a low(er) pressure (than normal)
We can see light from the Sun but we cannot hear any sound from it. State the reason for this.
light does not need a medium to travel through OR sound needs a medium to travel through (and there is no medium
between Sun and Earth)
State what is meant by monochromatic.
(light / electromagnetic radiation) of a single frequency
State two reasons why microwaves are used for mobile phone (cell phone) signals.
(microwaves) only need short aerials / antennas
(microwaves) penetrate (some) walls
Describe, with the aid of a diagram, how a digital signal differs from an analogue signal.
State two advantages of using digital signals rather than analogue signals
- digital (signal) consists of two values
analogue (signal) varies over a range (of values)
digital (signal) with blocks of high (1) and low (0) AND labelled diagram of analogue with continuously variable signal - faster (data) transmission rate OR data can be compressed
data / signal transmitted over long(er) distances (as signal can be regenerated)
noise easily removed (from signal / data) OR signal can be regenerated
State the types of wave that P-waves and S-waves can be modelled as.
P-waves: longitudinal
S-waves: transverse
Give two reasons why these two types of electromagnetic radiation are used in glass optical fibres for high-speed broadband
glass is transparent to visible light and (some) IR
(visible light and some IR) can carry high rates of data / information
how do you know if an image is virtual
Cannot be projected on a screen / light doesn’t pass through image
light / rays do not pass through I or
light / rays only seem to come from I or
produced by diverging rays
actual light rays do not meet at image OR light rays do not converge
Describe one use of X-rays in medicine
X-rays for detecting broken bones
X-rays pass through soft tissue AND not through bone
State two ways in which transverse waves differ from longitudinal waves.
particles (in transverse waves) vibrate perpendicular to the direction of travel (of the wave) OR
particles in longitudinal waves vibrate parallel to the direction of travel of the wave
longitudinal waves have compressions and rarefactions
transverse waves have troughs and crests
Explain why sound travels faster in water than in air
molecules closer together / water has greater density
State two properties of the image formed by the mirror.
virtual
upright
same size as object
laterally inverted
In the plastic, blue light travels slightly slower than red light and so the critical angle for blue light is smaller than the critical angle for red light. The laser that emits red light is replaced by one that emits blue light. Now blue light
enters the block at P and hits the straight edge at M.
Explain what happens to the blue light after it hits the straight edge at M
critical angle (for blue light) < 37° or critical angle for red (light) is 37°
angle of incidence (of blue light) greater than its critical angle (in plastic)
total internal reflection or all the (blue) light reflects or no (blue) light leaves the glass / refracts / travels in air along the straight edge
The frequency of the wave is increased to a value many times greater than the value obtained in (b).
Describe and explain two ways in which a diagram representing the wave with the greater frequency differs from Fig. 6.2.
compressions / rarefactions closer or more compressions / rarefactions (in same distance)
less diffraction / spreading out
(because of) smaller wavelength or ratio wavelength / gap width smaller ((wavelength large so diffraction large))
Another harbour has a much wider gap between its walls.
Describe and explain how the pattern of wave crests in this harbour is different from the pattern you have drawn in (i).
waves pass through gap remaining straight
less / no diffraction occurs
Iodine-131 emits γ-radiation. It has a half-life of 8 hours.
Explain why this emission and this half-life make iodine-131 a suitable material for a tracer in medical diagnosis.
- γ can be detected outside body
- needs long enough half-life to be detected / reach part of the body required
- needs short enough half-life to soon have very little activity
- gamma weakly ionising or pass out of body without harm
Explain, in terms of the behaviour of light rays, what is meant by principal focus for a thin converging lens.
State what is meant by focal length
- (point) where (parallel) rays (of light) meet (after passing through lens)
on principal axis
point) where parallel rays (of light) meet / are focussed (after passing through lens) or (point) through which rays (of light)
that emerge parallel pass (before reaching lens)
- distance between principal focus / focal point and optical centre / lens
Describe one medical use of X‑rays.
State one reason why it is necessary to take safety precautions when X‑rays are used.
- stated medical use (e.g. treating cancer / X-ray shadowgraph / sterilising equipment)
statement of what happens to the X-rays (e.g. absorbed by tumour / bones / bacteria)
stated consequence (e.g. tumour killed or image / picture / shadow / photograph produced)
- can cause burns / (cell) mutation / cell damage / tumours / cancer / damages DNA etc.
Describe an experiment to determine the speed of sound in air. State the apparatus you need, details of how to take measurements and how to calculate the speed of sound in air.
method of producing sound, e.g. clap for echo method or gun for direct measurement, sig gen or loudspeaker, hammer
on block
apparatus used, e.g. stopwatch, long tape, trundle wheel, wall if using echo method, metre rule, microphones and timer or microphones and oscilloscope
measure distance between person and the wall, measure distance between loudspeaker and microphone or measure distance between two microphones
appropriate time measured, e.g. at one end start stopwatch when smoke seen from gun and stop it when sound heard, start stopwatch when gun heard / clap heard and stop when echo heard, measure time taken between clap and hearing echo, timer starts when first microphone receives signal and stops when second receives signal
speed = measured distance / time for direct method
OR speed = 2 × distance from student clapping to wall / time for echo method OR distance between microphones = wavelength AND v = f × λ
Sound waves from a television are diffracted through doorways. Light waves from a television are not diffracted through doorways. Suggest why light waves and sound waves behave differently in this situation.
wavelength of light is (much) smaller than width of doorway or wavelength of sound
wavelength of sound is similar to width of doorway OR
λ ≃ width of gap for diffraction to occur OR larger wavelength
results in greater diffraction
Explain the term total internal reflection.
light travelling from optically dense medium to optically less dense medium (ight (must pass) from medium where it travels slower or to medium where it is faster or from medium with larger refractive index or to medium with smaller refractive index)
all light reflected OR no light refracted
angle of incidence is greater than the critical angle
(a) Explain why the direction of the wavefronts changes in the way shown in Fig. 6.1 (deep to shallow)
speed changes or (wave) speed is smaller in right-hand part of tank or waves slow down or bottom (on the page)
section of wave hits the boundary first
(wave) speed is smaller in right-hand part of tank or waves slow down or bottom (on the page) section of wave hits the
boundary first
bottom (on the page) / one part / one side / one section of wave slows down first (and different sections are delayed by
different amounts)
Describe and explain the action of optical fibres in communication technology. You may draw a diagram in your answer.
light / infrared travels in fibre
total internal reflection at inner surface or within (graded-index) fibre
light carries information / signal / data / message or signal / light encoded
State and explain the use of optical fibres in medicine
description of fibre passing to site to be examined / treated
light passes down fibre (to site) AND (image) returns (to sensor / observer) OR alternative use to endoscopy
extra detail, e.g. laser light source, illuminated organ, image, camera / type of sensor
State two uses for infrared radiation
remote controls
(infrared) sensors / alarms
specific electrical appliances
thermal imaging
X-rays are used in hospitals to help treat patients. Suggest and explain three precautions for the safe use of X-rays.
- shielding of operator behind screen / lead apron / out of room AND to absorb radiation
- shielding of other parts of patient with lead / shielding of other parts of patient AND to absorb radiation
- distance from source AND reduces intensity / amount of radiation / exposure
- limit time of exposure / not too frequent / max number of X-rays per year AND to limit dose
- limit strength / intensity of X-ray beam AND to limit dose
The light travels more slowly in the transparent solid.
(a) Explain, in terms of the wavefronts, why the light changes direction as it enters the solid. You may draw on Fig. 6.1 as part of your answer.
idea of one side of wavefront enters / hits solid first OR wavefront does not all hit the solid all at once;
idea of this side slowed down first OR this side delayed relative to other side
angle of wave(front) changes OR different parts of wavefront delayed by different amounts
real image
light passes through it OR can be projected/seen on a screen OR refracted rays cross/meet
Describe, with a labelled diagram, an experiment using water waves that shows the reflection of wavefronts that occur at a straight barrier.
Diagram to show: labelled barrier, incident straight or curved waves
Diagram shows appropriately reflected waves
Water surface e.g. tank of water/ripple tank/pond/acceptable alternative
How waves are produced: e.g., moving end or length of solid rod dipping into surface OR small solid object thrown in.
Detail of barrier: made of metal, glass or wood fixed in position
How observed: by eye, video, film, stroboscope
A dentist takes an X-ray photograph of a patient’s teeth. Explain why it is safe for the patient to be close to the source of X-rays, but the dentist must stand away from the source.
State, with a reason, why microwave ovens are designed only to work with the door closed.
X-rays ionising/harmful/dangerous (to humans)
Any one from:
patient rarely exposed
low total dose on patient
meaningful comment about benefit outweighs danger
dentist frequently exposed
total dose on dentist would be high if stayed in room
microwaves harmful/dangerous (to humans)
microwaves would pass through open door
Fig. 8.2 shows a spherical fishbowl, full of water, by a window. A black curtain hangs behind the fishbowl.
When full of water, the fishbowl can act as a converging lens.
Suggest one possible hazard of leaving the fishbowl next to the window in bright sunlight
(focused rays) set fire to curtain
State two uses of optical fibres.
- to carry (telephone) signals / communications
- for medical diagnosis / imaging
- specified artistic (display)
- specified lighting
State one other similarity between sound of frequency 750Hz and ultrasound.
State one way in which sound of frequency 750Hz is different from ultrasound.
longitudinal OR vibration parallel to wave travel direction OR transfer energy
frequency / pitch less OR below 20 000 Hz OR audible (to someone with normal hearing)
Explain what is meant by the term transverse wave motion.
transmission of energy (through medium) and no transfer of matter
(direction of) vibration of particles or (direction of) vibration of medium
perpendicular to direction of energy travel / wave / propagation
State the two types of radiation that are emitted by the heater.
infra-red and visible light
