dk paper 2

Question 1

emf vs pd

Answer 1

emf - energy gained per unit charge from power supply
pd - energy given away per unit charge to component

Question 2

potentiometer

Answer 2

varies voltage
- used as a variable resistor connected as a potential divider
+ can vary from 0 to max V

Question 3

rheostat

Answer 3

variable resistor
- can vary current as R varies
- can be connected as a potentiometer to very V with small I

coil of wire thats length is altered to alter R

Question 4

intensity prop to

Answer 4

KE
A^2

Question 5

cladding

Answer 5

lower n so TIR occurs
prevents crossover

Question 6

creating microwaves

Answer 6

transmitter has ac passed though at a certain freq
electric field created oscillates vertically creating microwaves at the same freq

Question 7

horizontal grille block vertically polarised microwaves

Answer 7

• the electric field caused due to microwaves is veritcal so cannot induce current in horizontal grille, so the wave is reflected or absorbed

Question 8

mauls law

Answer 8

I = I0 cos^2 theta

Question 9

arials

Answer 9

• mesh reflectes signal to front
• rod picks up signal
• adjacent emitted alternate between horizontal and vertical to avoid interference

Question 10

LED

Answer 10

electron transfered across pd
gains energy - excited
emits photon when it de excites
eV = hf

Question 11

photo electric effect - particles

Answer 11

• threshold freq
• no electrons prop to intensity after threshold freq
• variety of KE of electrons
• mas KE increases with freq NOT INTENSITY

Question 12

capacitor use

Answer 12

• releasing energy quick
• smoothing voltage
• storing energy

Question 13

oscilloscope (electron gun)

Answer 13

• electron gun produces beam of electrons
  electrons deflected by pd across x and y plates

Question 14

hall probe

Answer 14

measure magnetic flux density (B)
Vh = BI/nbq
b = thickness

Question 15

voltage due to hall effect

Answer 15

I = nAqv
F(B) = Bqv
F(E) = Eq
Bv = E
Bv = V/d
V = Bvd = BId/nAq = BI/nbq

Question 16

peak emf

Answer 16

V = d/dt (-NBAcoswt)
V = NBAw sinwt
max when NBA w

Question 17

transfromer losses

Answer 17

• current heating effect - decrease R
• magnetic losses - use soft core
• magnetising - use easily magnetised material
• eddy currents - laminate between layers

Question 18

neutrons discovered

Answer 18

Chadwick
alpha particles hit Be nuclei and knock off neutrons

Question 19

quarks class

Answer 19

up down
top bottom
charm strange
increase mass/ energy as go down

Question 20

cloud chamber

Answer 20

• air saturated with vapour at low temp
• when air molecules ionised liquid condenses and leaves tracks of droplets
• marks path of radiation

Question 21

transmutation

Answer 21

nuceli changes to another element when emitting alpha

Question 22

activity

Answer 22

rate of decay of nuclei

Question 23

decay constant

Answer 23

prob of decay of a nucleus per unit time

Question 24

+ CAT

Answer 24

• better contrast
• 3D

Question 25

capacitor dielectric use

Answer 25

electric field causes polar molecules to align with field reduces electric field strength between plates reduces pd across plates C = Q/V - Q constant so C increases

Question 26

EM wavelenghts

Answer 26

radio - km - m micro - mm infrared 10^-6 visible - 400-700nm UV 10^-8 X-ray 10^-10 gamma 10^-12