Waves and Materials

Question 1

Young Modulus

Answer 1

tensile stress/strain (assuming the limit of proportionality has not been exceeded). The unit of the Young modulus is the pascal (Pa) which is to 1 Nm^-2

Question 2

yield point

Answer 2

point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain

Question 3

ultimate tensile stress

Answer 3

tensile stress needed to break a solid material

Question 4

stiffness constant

Answer 4

the force per unit extension needed to extend a wire or a spring

Question 5

stress

Answer 5

force per unit area of cross section in a solid perpendicular to the cross section

Question 6

strain

Answer 6

extension per unit length of a solid when deformed

Question 7

Hooke’s Law

Answer 7

the extension of a spring is proportional to the force needed to extend it up to a limit referred to as its limit of proportionality

Question 8

elasticity

Answer 8

property of a solid that enables it to regain its shape after it has been deformed or distorted

Question 9

elastic limit

Answer 9

point beyond which a wire is permanently stretched

Question 10

breaking stress

Answer 10

tensile stress needed to break a solid material

( means the same as the ultimate tensile stress)

Question 11

brittle

Answer 11

snaps without stretching or bending when subject to stress

Question 12

transverse waves

Answer 12

The direction of oscillations are perpendicular to the direction of energy propagation

Question 13

Longitudinal waves

Answer 13

The direction of oscillations are parallel to the direction of energy propagation

Question 14

Young’s fringes

Answer 14

parallel bright and dark fringes observed when light from a narrow slit passes through two closely spaced slits

Question 15

Stationary wave

Answer 15

Wave pattern with nodes and anti-nodes formed by the superposition of two progressive waves of equal amplitude and frequency travelling in opposite directions

Question 16

amplitude

Answer 16

the maximuum displacement from equilibrium of an oscillating object. For a transverse wave it is the dstance from the middle to the peak of the wave

Question 17

antinode

Answer 17

fixed point in a stationary wave pattern where the amplitude is a maximuum

Question 18

coherent

Answer 18

two sources of waves are coherent if they emit waves with a constant phase difference

Question 19

critical angle

Answer 19

the angle of incidence of a light ray must exceed the critical angle for total internal reflection to occur

Question 20

cycle

Answer 20

interval for a vibrating particle (or wave) from a certain displacement and velocity to the next time the particle (or wave) has the same displacement and velocity

Question 21

diffraction

Answer 21

the spreading of waves when they pass through a gap or round an obstacle.

Question 22

diffraction grating

Answer 22

a plate with many closely ruled parallel slits on it

Question 23

dispersion

Answer 23

splitting of a beam of white light by a glass prism into colours

Question 24

ductile

Answer 24

stretches easily without breaking

Question 25

first harmonic

Answer 25

patten of stationary waves on a string when it vibrates at its lowest possible frequency

Question 26

frequency

Answer 26

the number of oscillations per second

Question 27

node

Answer 27

fixed point in a stationary wave pattern where the amplitude is zero

Question 28

period of a wave

Answer 28

time for one complete cycle of a wave to pass a point

Question 29

path difference

Answer 29

the difference in distances from two coherent sources to an interference fringe

Question 30

phase difference

Answer 30

the time between successive instants when two objects are at maximum displacement in the same direction

Question 31

plane-polarised waves

Answer 31

transverse waves that vibrate in one plane only

Question 32

progressive waves

Answer 32

waves which travel through a substance (or through space if electromagnetic)

Question 33

refraction

Answer 33

change of direction of a wave when it crosses a boundary where its speed changes

Question 34

refractive index

Answer 34

speed of light in free space

speed of light in the substance

Question 35

superposition

Answer 35

the effect of two waves adding together when they meet

Question 36

time period

Answer 36

time for one complete cycle of oscillations

Question 37

wavefronts

Answer 37

lines of constant phase (e.g. wavecrests)

Question 38

wavelength

Answer 38

the least distance between adjacent vibrating particles with the smae displacement and velocity at the same time