Oscillations/Wave Motion

Question 1

Define simple harmonic motion

Answer 1

Defined as a periodic motion where the acceleration’s object must always be directly proportional and opposite to the displacement from it’s equilibrium position

Question 2

Define the equilibrium position for wave motion

Answer 2

The midpoint of oscillation. The position where no net force acts on the particle.

Question 3

Define the displacement for simple harmonic motion

Answer 3

The distance from its equilibrium position in a specific direction.

Question 4

Define amplitude of simple harmonic motion

Answer 4

The maximum displacement from its equilibrium position.

Question 5

Define velocity of a particle in simple harmonic motion

Answer 5

The instantaneous velocity of the particle.

Question 6

At which position does the minimum speed of the particle occur, amplitude or equilibrium positions?

Answer 6

Amplitude position

Question 7

At which position does the maximum speed of the particle occur, the amplitude or equilibrium positions?

Answer 7

Equilibrium

Question 8

Define the acceleration of a particle in simple harmonic motion.

Answer 8

The instantaneous acceleration of the particle

Question 9

At which position does the minimum magnitude of acceleration occur, the amplitude or equilibrium positions?

Answer 9

Equilibrium position

Question 10

At which position does the maximum magnitude of acceleration occur, the amplitude or equilibrium positions?

Answer 10

Amplitude position

Question 11

Define the period of an oscillation

Answer 11

The time taken for the particle to complete one oscillation

Question 12

Define the frequency of an oscillation.

Answer 12

The number of oscillations performed per unit time

Question 13

Define phase/phase angle + the phase angle of one full cycle of an oscillation.

Answer 13

Phase/phase angle is the stage of oscillation the particle is in at a particular instant.

In one full cycle of an oscillation, the phase angle is 360° (2π rad), which also means it’s 0 rad since it reverts back to its original position.

Question 14

Define angular frequency of a particle in simple harmonic motion

Answer 14

The product of 2π and the frequency of oscillation of the body in simple harmonic motion

Question 15

At which position does max KE/min PE occur

Answer 15

The equilibrium position

Question 16

At which position does min KE/max PE occur

Answer 16

The amplitude positions

Question 17

What happens in a free oscillation?

Answer 17

The body oscillates under a resisting force only, without any external or resistive force acting on it; and the total energy of the oscillating body stays constant.

Question 18

Define damped oscillation

Answer 18

An oscillation where it’s amplitude gradually decreases as the body loses energy due to resistive forces.

Question 19

Define forced oscillating system

Answer 19

The body oscillates under a periodic driving force from a driver, where there is continuous energy input to the oscillating body.

Question 20

What are the 3 features of a resonance curve?

Answer 20

Curves shifted lower with increased damping (amplitude gets smaller)

Flatter peak at resonance with increased damping.

Peak is skewed to the left with increased damping.

Question 21

Define wave.

Answer 21

A wave is a propagation of a disturbance which transfers energy from one point to another without the physical transfer of matter.

Question 22

Define a progressive wave

Answer 22

Waves that transfer energy from one point to another without the transfer of matter.

Question 23

Define a transverse wave.

Answer 23

a wave where particles vibrate in a direction perpendicular to the direction of propagation of energy

Question 24

Define a longitudinal wave.

Answer 24

A wave where particles oscillate to the direction of propagation of the wave.

Question 25

Define the speed of a wave.

Answer 25

The distance travelled by the wave over the time taken.

Question 26

Define wavefront

Answer 26

The imaginary line joining all the points of the wave that have the same phase.

Question 27

Define the ray of a wave.

Answer 27

A ray is the line drawn in the direction of the wave motion which is used to indicate the path taken by the wave.

Question 28

Define the intensity of a wave

Answer 28

The rate of transfer of energy per unit area perpendicular to the direction of the wave.

Question 29

The 6 formulae for intensity of a wave

Answer 29

E/tA P/A P/(4πr^2) P/(2πr) kA^2 K(f^2)(A^2)

Question 30

Define polarization of a wave

Answer 30

The process whereby vibration of the particles of a transverse wave occurs in a single plane only, and the direction of the vibrations are perpendicular to the direction of propagation of the plane.

Question 31

Malu's law

Answer 31

The intensity of a beam of plane-polarized light after passing it through a polarizer varies with the square of the cosine of the angle through which the polarizer is rotated from the position that gives maximum intensity.

Question 32

Formula for the intensity of a transmitted wave (through a polarizer)

Answer 32

I = I(max) (cos theta)^2

Question 33

The resultant amplitude A of light transmitted through a polarizer:

Answer 33

A = A(max) (cos theta)^2

Question 34

For an oscillating body, state what is meant by forced frequency.

Answer 34

The frequency at which the body is made to vibrate or oscillate when a periodic external force acts on it.

Question 35

For an oscillating body, state what is meant by natural frequency of vibration

Answer 35

The frequency at which the body is made to vibrate or oscillate freely without any extreme or resistive force acting on it.

Question 36

For an oscillating body, state what is meant by resonance.

Answer 36

Resonance is the maximum transfer of energy from the driver to the body during a forced oscillation, where the body oscillates with max amplitude, and when the driving frequency is equal to the natural frequency of vibration.

Question 37

State and explain one situation where resonance is useful

Answer 37

Cooking of food using microwave oven: microwaves having a frequency the same as the natural frequency of vibration of water molecules in food is used to cook the food

Question 38

State and explain one situation where resonance should be avoided.

Answer 38

On vibrating machinery parts, metal panels on the body of a washing machine resonates when driving frequency of the rotating drum is equal to the natural frequency of the panel.

Question 39

What happens during light damping

Answer 39

The amplitude of oscillations gradually decreases with time but the period remains constant.

Question 40

For an oscillating body, state what is meant by free oscillations

Answer 40

The body oscillates under a restoring force only without any external or resistive force acting on it

Question 41

Define forced oscillations in an oscillating system

Answer 41

The body oscillates under a periodic driving force from a driver where there is continuous energy input in a body.

Question 42

Why can't sound waves be polarized?

Answer 42

Sound waves are longitudinal waves which cannot be polarized no matter how the transmission axis of the polarizer is oriented, because the direction of vibrations of sound waves are parallel to the direction of propagation.

Question 43

For sound waves in the gas, state the origin of the energy in the wave.

Answer 43

The mechanical energy (KE and PE) of the vibrating source that produces the wave

Question 44

For sound waves in the gas, state the origin of the restoring force on a molecule as it vibrates.

Answer 44

The intermolecular forces between the neighbouring molecules to bring them back to equilibrium position.

Question 45

Explain why the intensity of a minimum is never zero.

Answer 45

As microwaves travel away from the source/gets reflected, the waves lose energy and amplitude decreases. Minimum corresponds to a node. When incident microwaves of relatively larger amplitudes superimpose with reflected microwaves of smaller amplitudes, resultant displacement ≠ 0 since it's unable to cancel out. As I is proportional to A², intensity at a minimum is never zero.

Question 46

Prove SHM using equations

Answer 46

ΣF= ma K(eo - x) - mg = ma where mg = keo -kx = ma a = (-k/m)x

Question 47

Derive v = fλ

Answer 47

speed = distance/time taken v = d/t = λ/T = fλ

Question 48

Order of magnitude of wavelengths in the electromagnetic spectrum

Answer 48

Radio > 1x10^-1 Micro 1x10^-3 to 1x10^-1 Infrared 7x10^-7 to 1x10^-3 Visible 4x10^-7 to 7x10^-7 Ultraviolet 1x10^-9 to 4x10^-7 X ray 1x10^-11 to 1x10^-9 Gamma < 1x10^-11