Waves

Question 1

Travelling Mechanical Wave

Answer 1

a disturbance carrying energy through a medium without any overall motion of that medium

Question 2

Travelling wave

Answer 2

either mechanical or electromagnetic, is a disturbance that travels out from the source producing it, transferring energy from the source to other places through which it passes

Question 3

Transverse wave

Answer 3

where the direction of vibration is perpendicular to the direction in which the wave travels

Question 4

Longitudal wave

Answer 4

where the direction of vibration is parallel to the direction in which the wave travels

Question 5

Unit of Frequency

Answer 5

Hertz (Hz) where 1 Hz= 1 cycle per second 1s^-1

Question 6

Reflection

Answer 6

The bouncing of waves off an obstacle in their path is called reflection of waves

Question 7

Refraction

Answer 7

The changing of direction of a wave when it enters a region where its speed changes

Question 8

Diffraction

Answer 8

The sideways spreading of waves into the region beyond a gap or around an obstacle

Question 9

Interference

Answer 9

When waves from two sources meet a new wave is produced. The displacements that produced at any point by this wave is the algebraic sum of the displacements that each wave would produce on its own. This is called the interference of waves.

Question 10

Constructive interference

Answer 10

when waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves, the waves are said to undergo constructive interference

Question 11

Destructive interference

Answer 11

when waves from two sources meet and the amplitude of the resulting wave is less than the amplitudes of each of the individual waves, the waves are said to undergo destructive interference

Question 12

coherant sources

Answer 12

two sources of periodic waves are said to be coherant if they are in phase or there is a constant phase difference between waves from each sources. If this is so the sources must also have the same frequncy

Question 13

Interference pattern

Answer 13

when waves from two or more coherant sources meet the resulting wave pattern formed an interference pattern

Question 14

stationary waves

Answer 14

when two periodic travelling waves of the same frequency and amplitude moving in opposite directions meet they interfere with each other. The resulting wave formed is called a stationary wave.

Question 15

The Doppler Effect

Answer 15

The apparent change in the frequency of waves due to the motion of the source or the observer is called the doppler effect. If a source emits waves of frequency f, the observed frequency f’

greater than f = source moves towards observer
less than f= source moves away from observer

Question 16

Doppler effect towards

Answer 16

f’=fc/(c-u)

Question 17

Doppler effect away

Answer 17

f’=fc/ (c+u)

Question 18

overtones

Answer 18

frequencies which are multiples of a certain frequency are called overtones of that frequency. If f is a given frequecy, 2f is the first overtone, 3f is the second overtone

Question 19

Loudness

Answer 19

loudness of a sound wave dpends on the amplitude of the sound wave. The greater the amplitue the greater the loudness

Question 20

Pitch

Answer 20

The pitch of a note depends n the frequency of the sound wave. The higher the frequecny, the higher the pitch, the lower the frequency the lower the pitch.

Question 21

Quality

Answer 21

the quality of a musical note depends on the number of overtones present in the note and the relative sstrengths of the different overtones present

Question 22

Frequency limits of audibility

Answer 22

The frequency limits of audibility are the highest and lowest frequencies audible by a human ear. The normal range is 20 Hz - 20 000 Hz

Question 23

Resonance

Answer 23

If the frequency of a periodic force applied to a body is the same or very near to its natural frequency, that body will vibrate with very large amplitude. This phenomenon is called resonance

Question 24

Sound Intensity at a point

Answer 24

is the rate at which sound energy is passing through unit area at right angles to the direction in which the sound is travelling at that point
Intensity =Power/Area

Question 25

Units of sound intensity

Answer 25

watts per square metre (Wm^-2)

Question 26

Threshold of hearing

Answer 26

The smallest sound intensity detectable by the average human ear at a frequency of 1000 Hz. Its value is 1 x 10^-12 Wm^-2

Question 27

Sound intensity level

Answer 27

measured in decibels

Question 28

Fundamental frequency of a string

Answer 28

a string vibrating with an antinode at its centre and a node at each end and no other nodes and antinodees is vibrating at its fundamental frequency.

Question 29

Harmonics

Answer 29

frequencies which are multiples of a certain frequency f are called harmonics. f is the fundamental frequency or the first harmonic. 2f is the second harmonic. 3f is the third harmonic. etc.

Question 30

The grating constant

Answer 30

the distance d between two adjacent slits (i.e. the width of one line and one slit) on the grating is called the grating constant or the grating spacing.

Question 31

The fact that light can be polarised shows…

Answer 31

that light is a transverse wave

Question 32

Dispersion

Answer 32

The separating out of the different wavelengths present in light is called dispersion

Question 33

Primary colours

Answer 33

Red green and blue

Question 34

Secondary colour

Answer 34

when two primary colours are mixed in equal intensity, the colour formed is a secondary colour e.g. yellow cyan and magenta

Question 35

complementary colours

Answer 35

a primary colour and a secondary colour that when mixed give white are called complementary colours