3. Waves (12-15)

Question 1

waves transfer

Answer 1

waves transfer energy without transferring matter

Question 2

Describe the features of a wave in terms of wavefront, wavelength, frequency, crest, trough, amplitude and wave speed, period

Answer 2

wavefront- a line joining adjacent point on a wave that are all in step with each other (separation of wavelength from trop)

wavelength- the distance bw 2 adjacent C/T of a wave

frequency- no. of waves passing on a point in one second

crest- the highest point of a wave
trough- the lowest point of a wave

amplitude- distance from undistributed level to C/Tof a wave

wave speed- the speed at which a wave travels

period- time taken for one complete wave to pass a point

Question 3

equation for wave speed and period

Answer 3

v = fλ ; wave speed= frequency * wavelength

T=1/f ; period (s) = 1/ frequency (Hz)

Question 4

Describe transverse and longitudinal wave with examples

Answer 4

1. transverse wave- the direction of vibration is at right angles to the direction of propagation

Ex- electromagnetic radiation, ripples on water and seismic S-waves (secondary)

crest & trough, travel- SL, den press- constant

2. longitudinal wave- the direction of vibration is parallel to the direction of propagation

Ex-sound waves and seismic P-waves (primary)

compression & rarefaction, travel- SLG, den press- changes

Question 5

Describe how waves can undergo:

(a) reflection at a plane surface

(b) refraction due to a change of a speed or change in speed caused by a change in depth

Answer 5

(a) A wave hits bw two media and stays in og medium- bounce away at same angle they strike in.
angle of i=angle of r.
speed, wavelength, frequency unchanged.

(b) when waves enter a dif medium, it changes direction.
frequency same, wavelength & speed changes

deep to shallow- wavelength and speed less, i>r, towards normal, bunch together

shallow to deep- wavelength and speed more, r>i, away from normal, spread out

deep- denser so denser to rarer medium- slow down.
* emw speed up from denser to rarer medium- light

Question 6

Describe how waves undergo:

(a) diffraction due to a gap

(b) diffraction due to an edge

Answer 6

waves spread out as it travels through a gap or past the edge of an object

(a) Diffraction due to a Gap: Waves undergo diffraction when they pass through a gap because the size of the gap is comparable to or smaller than the wavelength of the waves, causing them to bend and spread out.

(b) Diffraction due to an Edge: When waves encounter an edge, they diffract because the edge acts as a secondary source of waves, causing the original wavefronts to bend around it and create a diffraction pattern.

Question 7

Describe how wavelength and gap size affects diffraction through a gap and at an edge

Answer 7

wavelength- greater= greater angle at which diffracted at edge

gap- greatest effect when width of gap = wavelength of ripples.

significantly small gap- no diffraction
larger gap- less diffraction

Question 8

Define the terms normal, angle of incidence, angle of refraction and angle of reflection & state law of reflection

Answer 8

the line drawn at right angles to a surface at the point where ray hits the surface.

angle bw incident ray and normal drawn at a point where the ray hits the surface

angle bw reflected ray and normal drawn at a point where the ray hits the surface

angle bw refracted ray and normal drawn to the surface at the point where it passes from one medium to another. refraction- bending of light when passes from….

the angle of incidence is equal to the angle of reflection

Question 9

Describe the formation of an optical image by a plane mirror, and give its characteristics

Answer 9

same size, same distance from mirror, virtual

Question 10

Define refractive index, n with equation

Answer 10

the ratio of the speeds of a wave in two different regions.

n = sini/sinr
n = 1/sinc
n= speed of light in air/ speed of air in object

Question 11

Describe critical angle, internal reflection and total internal reflection

Answer 11

Critical angle- the minimum angle of incidence at which TIR occurs. angle of incidence is greater than critical angle.

IR- when a ray of light strikes the inner surface of a material and some of it reflects back inside it.

TIR- when a ray of light strikes the inner surface of a material and 100% of it reflects back inside it. denser to less dense

Question 12

Describe the use of optical fibres, particularly in telecommunications

Question 13

Describe the passage of light through a transparent material

Question 14

Describe the action of thin converging and thin diverging lenses on a parallel beam of light

Answer 14

a thin converging lens brings parallel light rays together at a focal point, while a thin diverging lens causes the light rays to spread out as if they are coming from a focal point

Question 15

Define the terms focal length, principal axis and principal focus (focal point)

Answer 15

focal length- the distance from the centre of the lens to its principal focus

principal focus- the point at which rays of light parallel to the principal axis converge after passing through a converging lens.

principal axis- the line passing through the centre of the lens perpendicular to its surface.

Question 16

Describe the characteristics of an image

Answer 16

beyond 2F- real, inverted diminished- bw 2F (other side)

At 2F- real, inverted same size- at 2F (other side)

bw 2F and F- real, inverted, enlarged- beyond 2F (other side)

At F- no image

bw F & principal axis- virtual, upright, enlarged- in front of focal point (object’s side of lens)

Question 17

Describe the use of a single lens as a magnifying glass

Answer 17

Magnifying glass is a converging lens.

image is upright, enlarged, virtual and further from the lens than object

Question 18

how is a virtual image is formed

Answer 18

diverging rays are extrapolated backwards and does not form a visible projection on a screen

Question 19

Describe the use of converging and diverging lenses

Answer 19

correct long-sightedness and short-sightedness

SS- person cannot see clear image of distant objects. long eyeball so rays meet in front of retina and image is formed there. diverging lens- increases focal length of eye and brings focal point backward so that rays converge on retina.

LS- person cannot see clear image of close objects. long eyeball or lens not strong enough so rays cannot converge and image is formed behind retina.
converging lens in front of eye lens-reduces focal length of eye OR converging lens brings focal point forward (so that) rays converge / focus on retina

Question 20

Describe the dispersion of light

Answer 20

the separation of different colours of light because they are refracted through different angles

Question 21

seven colours of the visible spectrum with pattern

Answer 21

red, orange, yellow, green, blue, indigo, violet

increasing frequency
VIBGYOR- increasing wavelength

violet light is bent the most while red light is bent the least- violet light has a shorter wavelength, it is slowed more than the longer wavelengths of red light

Question 22

monochromatic

Answer 22

visible light of a single frequency

Question 23

main regions of the electromagnetic spectrum in order of frequency, speed and in order of wavelength

Answer 23

roman men invented very unusual x-ray guns
radio, micro, infrared, visible light, ultraviolet, x-ray, gamma

increasing frequency and decreasing wavelength speed same 3.0 × 10^8 m/s in vacuum and air

Question 24

Describe typical uses of the different regions of the electromagnetic spectrum

Answer 24

(a) radio waves; radio and television transmissions, astronomy, radio frequency identification (RFID)

(b) microwaves; satellite television, mobile phones (cell phones), microwave ovens

(c) infrared; electric grills, short range communications such as remote controllers for televisions, intruder alarms, thermal imaging, optical fibres

(d) visible light; vision, photography, illumination

(e) ultraviolet; security marking, detecting fake bank notes, sterilising water

(f) X-rays; medical scanning, security scanners

(g) gamma rays; sterilising food and medical equipment, detection of cancer and its treatment

Question 25

Describe the harmful effects on people of excessive exposure to electromagnetic radiation,

Answer 25

(a) microwaves; internal heating of body cells

(b) infrared; skin burns

(c) ultraviolet; damage to surface cells and eyes, leading to skin cancer and eye conditions

(d) X-rays and gamma rays; mutation or damage to cells in the body

Question 26

communication with artificial satellites is mainly by

Answer 26

microwaves

(a) some satellite phones use low orbit artificial satellites

(b) some satellite phones and direct broadcast satellite television use geostationary satellites

Question 27

many important systems of communications rely on

Answer 27

electromagnetic radiation including:

(a) mobile phones (cell phones) and wireless internet use microwaves because microwaves can penetrate some walls and only require a short aerial for transmission and reception

(b) Bluetooth uses low energy radio waves or microwaves because they can pass through walls but the signal is weakened on doing so

(c) optical fibres (visible light or infrared) are used for cable television and high-speed broadband because glass is transparent to visible light and some infrared; visible light and short wavelength infrared
can carry high rates of data

Question 28

difference between a digital and analogue signal

Answer 28

digital (signal) consists of 1(s) and 0(s) / high value and low analogue (signal) is (continuously) variable (in magnitude)

Question 29

a sound can be transmitted as a digital or analogue signal. why and how

Answer 29

A sound wave is an analogue signal- it can vary continuously.

Question 30

Explain the benefits of digital signaling

Answer 30

increased rate of transmission of data and
increased range due to accurate signal regeneration

Question 31

production, nature of sound, how it’s cause and its range

Answer 31

sound is produced by vibrating sources

a medium is needed to transmit sound waves

longitudinal nature of sound waves- source of sound vibrates and causes air particles around to vibrate back and forward in direction sound is travelling. It consists of compression and rarefaction cause change in pressure.

range of frequencies audible to humans- 20 Hz to 20 000 Hz

Question 32

Compression and rarefaction

Answer 32

C- region where particles are closer together than normal & region where there is a greater pressure than normal

R- region where particles are further apart than normal & region where there is a lower pressure than normal

Question 33

speed of sound in different states

Answer 33

speed of sound in air is 330–350 m/s
liquid- 1500 m/s
solid- 6000 m/s

sound travels faster in solids than in liquids and faster in liquids than in gases

Question 34

Describe a method involving a measurement of distance and time for determining the speed of sound in air

Answer 34

Method 1:
Long distance / distance in field measured with the tape One student fires pistol at one end (of this distance) Student at other end starts stop-watch on seeing smoke / light from pistol and st /
ops stop-watch on hearing sound of pistol speed = (measured) distance / (measured) time

Method 2:
Distance of 50 m or more from a vertical wall measured with the tape
Student 1 fires pistol at this distance from the wall Student 2 standing next to student 1 starts stop-watch on hearing pistol and stops stop-watch on hearing echo speed = 2 × (measured) distance / (measured) time

Question 35

Describe how changes in amplitude and frequency affect the loudness and pitch of sound waves

Answer 35

large amplitude- louder

high frequency- high pitch (short wavelength)

Question 36

Describe an echo and ultrasound with its uses. last flashcard.

Answer 36

the reflection of sound waves

sound with a frequency higher than 20 kHz

non-destructive testing of materials, medical scanning of soft tissues and sonar

Question 37

Describe how the cone of the loudspeaker produces this sound.

Answer 37

it / cone vibrates

any two from:
alternating current (a.c.) (in coil /wire) or alternating magnetic field

(neighbouring) air vibrates or vibrations passed on

(producing) compressions and rarefactions / vibrations parallel to energy transfer

vibrating at 15 000 Hz

Question 38

State how the speed of light in glass depends on its frequency. Explain how this is shown by the dispersion of white light in the prism

Answer 38

larger frequency results in smaller speed (in glass) or r.a. (reverse argument) or inversely related / proportional.

any two from:
more refraction / closer to normal / larger refractive index for larger frequency or r.a.

violet light has larger frequency or o.r.a.

violet light has a smaller speed (in glass) or o.r.a.

violet light has larger refractive index or o.r.a.

Question 39

The wave travels from the rock into the air.

State and explain whether the wave will be audible to a healthy human ear.

Answer 39

frequency not changed (in different medium)
audible / yes AND audible range 20 Hz – 20 kHz

Question 40

(a) Fig. 6.1 shows an empty container and an observer’s eye. There is a small coin at position O. The observer is unable to see the coin. The observer and the coin stay in the same position and the container is filled with water. The observer can now see the coin.

(i) Explain why the coin can be seen by the observer.

Answer 40

{light from water OR light to air / eye OR light from coin} bends / changes direction / is refracted

refracts / bends away from normal OR angle of incidence is smaller than angle of refraction

Question 41

The loudness of the sound increases at the same pitch.

State and explain any change there would be in the pattern of wavefronts shown in Fig. 6.1.

(d) The wave passes into water. State and explain any change in the pattern of wavefronts shown in Fig. 6.1.

Answer 41

closer together at compression and further apart at rarefaction
amplitude changes
loudness does not affect wavelength

6(d) more spread out / further apart
Velocity / speed greater in water than air
(so) wavelength greater

Question 41

Images formed by lenses sometimes have coloured edges.
Suggest a reason for this.

Answer 41

different colours have different wavelengths / different frequencies / refracted by different amounts OR dispersion (in glass)