PHU-Waves and the particle nature of light

Question 1

Define a wave period

Answer 1

Time taken to complete one oscillation

Question 2

Give the two formulas for frequency

Answer 2

Frequency=no.oscillations/time or frequency=1/period

Question 3

Polarized wave?

Answer 3

Must be TRANSVERSE. This is where the electric field is only oscillating in one direction

Question 4

How do polarizers work?

Answer 4

Only allow transverse waves at particular angles to pass through

Question 5

Briefly explain how Polaroid sheets work

Answer 5

Made of long molecules of quinine indosulphate which run up and down the sheet. Any polarization direction parallel to sheet is absorbed. Any perpendicular is transmitted at a lower intensity.

Question 6

Define the two types of wave

Answer 6

Mechanical:needs a medium-substance that oscillates
EM:don’t need a medium- oscillations of electric and magnetic fields

Question 7

Aerials for transmission & reception

Answer 7

Tv/radio aerial can be orientated so spokes are vertical/horizontal.
(If a transmitter sends out a vertically polarized wave, aerial spokes must also be aligned vertically for MAXIMUM ABSORPTION-needed for a good signal)

Question 8

How are stationary waves formed?

Answer 8

Formed when two progressive waves (same frequency+wavelength) moving in opposite directions interfere with each other.

Question 9

What DON’T stationary waves do?

Answer 9

Transfer energy from one place to another

Question 10

What are nodes and antinodes?

Answer 10

nodes: points on waves with zero amplitude
antinodes: points on waves with maximum amplitude

Question 11

What are resonant frequencies?

Answer 11

stationary waves have certain frequencies called resonance frequencies ONLY at which they can happen

Question 12

When do resonant frequencies happen?

Answer 12

When the distance between the two fixed ends is a multiple of 1/2λ

(E.g:first resonant frequency=1st harmonic- happens when the distance between the 2 fixed ends=1/2λ: has 2 nodes & 1 antinode)

Question 13

How do bats use pulse-echo measurements?

Answer 13

-emit chirp of 50-100kHz through nose lasting about 3 milliseconds
-reflects of object up to 50km away (further echo is too attenuated)
-sensitive ears+brain measure time delay and v=xt

Question 14

How do humans use pulse-echo measurements?

Answer 14

-ranging and imaging systems
-sonar on ships + submarines
-particularly useful when other methods are dangerous and hazardous (surface of venus)

Question 15

Relationship between frequency,wavelength and resolution?

Answer 15

higher frequency=shorter wavelength=greater resolution

Question 16

Give the 2 formulas for intensity with units

Answer 16

I=p/A or I=p/4πr^2 where intensity is measured in w/m^2

Question 17

What happens to radiant power when a wave spreads out uniformly from source?

Answer 17

It will spread out uniformly

Question 18

Describe the relationship between intensity to the square of the amplitude

Answer 18

I∝A^2

Question 19

Give two examples of longitudinal and transverse waves

Answer 19

Longitudinal: P-waves & sound
Transverse: S-waves & any em waves

Question 20

Which seismic waves can’t travel through liquids?

Answer 20

s-waves