jan mocks dk paper 2

Question 1

electron gun

Answer 1

• speeds up electrons with accelerating pd
• thermionic emissions cause electrons to escape
• attracted to anode

Question 2

internal resistance

Answer 2

resistance due to the material the battery is made from
causes energy to be wasted as heat

Question 3

battery charger

Answer 3

connect a charger with a higher emf to the battery
forces current into the battery to charge it

Question 4

potentiometer

Answer 4

varies voltage
vary output V from fixed supply - 0>maxV

Question 5

rheostat

Answer 5

can be connected as a variable resistor - good if large I needs to be varied
or can be connected as potentiometer to vary V - currents are very small

Question 6

intensity prop to

Answer 6

A^2
v^2
KE
v prop to A

Question 7

how signals are sent

Answer 7

amplitude modulated
- amplitude shows messgae
freq modulated
- freq of wave shows message wave

Question 8

arials

Answer 8

• mesh reflects signals to front
• circular rod picks up signal (1/2λ tall)
• other rods boost signal (1/2λ apart)
• adjacent emitters alternate between hor and ver to avoid interference if they overlap signal areas

Question 9

measuring λ of microwaves

Answer 9

• probe is moved from central maxima along
• positions marked and path diff determined
• each max can be used to calc λ then average

Question 10

youngs double slit - set up + risks

Answer 10

• pass through colour filter (monochromatic)
• creates fringes
  risks
• dont look at laser
• remove reflections
• dark room

Question 11

diffraction grating

Answer 11

more slits = narrower bands
d sinθ = nλ
nmax = d/λ

Question 12

photons

Answer 12

quanta of energy of electromagnetic radiation

Question 13

LED

Answer 13

• electron transferred across pd
• gains energy
• emits energy as a photon
  eV = hf
  plot eV against f
  grad = h

Question 14

conc for photoelectric effect - not wave theory

Answer 14

• only emit above threshold freq
• intensity doesn’t effect energy
• no. electrons prop to intensity after f>f0
• electrons emitted have a variety of KE up to max
• max KE ^ with f

Question 15

find max KE of emitted electrons

Answer 15

find stopping voltage
eV = max KE = hf -hf0

Question 16

diffraction rings

Answer 16

grating
nλ = d sinθ
if v ^ rings get smaller/ closer
d = spacing between atoms
λ = h/mv

Question 17

curved accelerators

Answer 17

• increased r = increased acceleration
• curved - particles accelerate through gaps more than once
  + particles can reach higher energy - keep going round
  + alternating field keeps giving more energy

Question 18

hall probe

Answer 18

• measures mag flux density
• Vh = BI/nbq
  where b = thickness

Question 19

hall effect

Answer 19

• pd created across a semi conductor due to mag field across it
• when wire in field - force occurs due to field -as electrons move down
• electric field created
• when eq F(E) = F(B)
• travel in straight line

Question 20

lenz law

Answer 20

direction of induced emf due to change in flux linkage
is such that it would oppose the change producing it

Question 21

ac generator

Answer 21

• consists of coil spun in uniform field
• when coil spins at steady rate flux changes continuously
• when at θ linkage = NBAcosθ = NBAcoswt
• emf = NBAw sinwt
  max emf = NBAw

Question 22

emf in terms of v

Answer 22

v = BA = BLs/t = BLv

Question 23

why transformers not 100% efficient

Answer 23

• loss from current flowing - resistance causes heating effect Ploss = I^2R
• loss from magnetic losses
• loss from magnetising increases temp
• eddy currents created in iron core due to magnetic field causing electrons to move

Question 24

how to make more efficient

Answer 24

• decreasing resistance
• prevent coils close to soft core
• use material easily magnetised/ demagnetised
• laminated (insulator between layers)

Question 25

size of atom/ nucleus

Answer 25

nucleus = 10^-14
atom = 10^-10

Question 26

neutrons discovered

Answer 26

chadwick notices alpha particles hitting nuclei know off neutrons

Question 27

EM wavelengths

Question 28

EM freq

Question 29

mauls law

Answer 29

I = I0 costheta