important experiments (all topics p1 & p2) Flashcards

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1
Q

outline the stopping voltage set up

A

set up a circuit with a variable supply, ammeter, resistor and two separate metal plates under incident em radiation

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2
Q

capacitor circuit

A

parallel circuit with a switch across the two loops. cell and capacitor in one loop. resistor and (same) capacitor in the second.

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3
Q

explain the stopping voltage experiment

A
  • photons arriving at the metal plate cause photoelectrons to be emitted (if above threshold frequency) and crossing to the second metal plate
  • as the voltage of the supply is decreased it decreases the potential over the two plates. the photoelectrons must do work to overcome this.
  • the voltage at which the photoelectrons can no longer reach the other plate and turn around is the stopping voltage
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4
Q

stopping potential

A

The stopping potential is defined as the potential necessary to stop any electron (or, in other words, to stop even the electron with the most kinetic energy) from reaching the other side

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5
Q

what does the stopping voltage tell you

A

eV = 1/2mv^2
you can work out the work function from this
(W = QV)

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6
Q

verifying coulombs law

A
  1. charge insulating rods and measure their charge using a coulomb meter
  2. place one rod on the top tap balance and zero the scale
  3. bring the second rod close to the first and measure the change in mass
  4. repeat, changing either radius of rod or charges
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7
Q

finding the internal resistance of a power supply

A
  1. measure the terminal pd
  2. vary the current by changing the load resistance
  3. plot V agaisnt I the gradient is internal resistance, the y intercept is the emf
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8
Q

finding the resisitivty

A
  1. measure the diameter of the wire
  2. measure the voltage and current for various lengths of the same wire
  3. calculate the resistances
  4. plot resistance against length the gradient is resistivity/area
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9
Q

Boyles law experiment

A
  1. slowly use the foot pump to increase the pressure
  2. record the volume for different pressure level
  3. plot p agaisnt 1/v, if the graph is directly proportional it follows boyles law
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10
Q

Charles Law experiment

A
  • record the volume and temperature of the cold water
  • heat the water and record the temperatures
  • plot volume agaisnt temperature. If the graph is straight line and approximately crosses the x-axis at -273 degrees it follows Charles law
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11
Q

Gay Lussacs experiment

A
  1. heat is applied to the cylinder
  2. measure the temperature and volume at regular intervals
  3. plot P agaisnt T if its a straight line graph then it obeys the law
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12
Q

How does gay lussacs and charles experiments give evidence for an absolute zero temperature

A

They should be directly proportional however they are not and both intersect the x axis at -273. This gives evidence for the kelvin temperature scale where 0K is absolute zero.

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13
Q

Rutherford’s scattering experiment

A

A stream of alpha particles from a radioactive source were fired at a very thin gold foil sheet. The number of alpha particles at different angles was recorded

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14
Q

Rutherford’s scattering experiment conclusions

A
  • most (fast charged) alpha particles went straight through therefore an atom in mostly empty space
  • some alpha particles deflected at an angle greater than 90 therefore part of the atom must be more massive than the alpha particle this is the nucleus
  • alpha particles were repelled therefore the nucleus must be positively charged
  • since atoms are neutral overall so electrons must be in the outside of the atom
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15
Q

trigonometric parallax

A

The star is viewed from two positions at 6 month intervals
The change in angular position of the star against background of fixed stars
is measured
Trigonometry is used to calculate the distance to the star
The diameter/radius of the Earth’s orbit about the Sun must be known

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16
Q

distance to stars standard candles

A

the standard candles flux/intensity is measured. Use the inverse square law I = L/4πd^2 to calculate the distance.

17
Q

how to find plancks constant?

A
  • set up a potential divider circuit with a paralell section with different coloured LEDs, an ammeter and a voltmeter
  • measure the voltage and record the wavelength (read from packet)
  • plot a graph of v agaisnt 1/λ
  • the gradient equals Vλ
  • substitute E = eV into E =hc/λ input values and rearrange to get h
18
Q

what experiment determines the work function of different materials and the value of h?

A

stopping voltage experiment

19
Q

What does the graph from the stopping voltage experiment show?

A

gradient = h
F0 (x intercept) = threshold frequency
y intercept = work function

20
Q

What does the y intercept from the stopping voltage experiment show?

A

the voltage needed to stop an electron being liberated by light of 0 frequency and so 0 energy (the work

21
Q

What axises are plotted from the stopping voltage experiment?

A
y = stopping voltage 
x = frequency
22
Q

locating the CoM of an object

A
  1. put holes in the object and hang it from a nail with a plumline and a weight of it
  2. hang the shape from the three pivots
  3. trace along the plumline with a pen
  4. where the lines cross is the CoM
23
Q

if you change charge when verifying coulombs law the charge force graph should be

A

a straight line through the origin

24
Q

if you change radius when verifying coulombs law the radius force graph should be

A

a 1/x curve

25
Q

measuring the resisitivity circuit

A

potential divider circuit with voltmeter and ammeter

26
Q

measuring internal resistance circuit

A

voltmeter in paralell over supply

resistor and ammeter in series

27
Q

measuring internal resistance graph

A

Voltage y axis
Current x axis
gradient internal resistance
y intercept emf

28
Q

measuring the young modulus

A
  1. measure the diameter of the wire
  2. thread the wire over the pulley, mark a point on the wire
  3. add masses and record how much it extends by
  4. measure stress and strain for these values and plot stress against strain, YM is the gradient
29
Q

how is the photoelectric effect shown?

A

by a gold leaf electroscope

30
Q

how does a gold leaf electroscope show the photoelectric effect

A

a charge is given to the electroscope, like charges repel so the gold leaf lifts up. if photons of the right frequency liberate the electrons the gold leaf will drop.

31
Q

if the p.d. in a stopping voltage experiment is increased what happens?

A

electrons are accelerated faster as they move in the same direction as the current

32
Q

if the pd. in a stopping voltage experiment is decreased what happens?

A

the battery is more effective than the photoelctric effect therefore the electrons are slowed and start to move backwards.