CPACs

Question 1

determine the acceleration of a freely falling object

Answer 1

1. set of two light gates to measure time and and an electromagnet on a stand
2. measure the distance between the light gates
3. release the steel ball from the electromagnet
4. repeat for different distances between the light gates
5. using s = ut + 1/2at^2 plot 2s/t agaisnt t. The gradient is the acceleration

Question 2

determine the acceleration of a freely falling object control variables

Answer 2

• The distance from the point of release and the first light gate
• the mass of the object / the object

Question 3

Why use and electromagnet in ‘determine the acceleration of a freely falling object’

Answer 3

It means there is no force of propulsion so SUVAT can be used

Question 4

risks in ‘determine the acceleration of a freely falling object’

Answer 4

• falling objects, put padding on the falling region

- tall unstable object, clamp to the table

Question 5

Sources of uncertainty in ‘determine the acceleration of a freely falling object’

Answer 5

• make sure the ruler is exactly vertical

- normal resolution uncertaintities

Question 6

Determine the electrical resistivity of a material

Answer 6

1. Set up the wire in a circuit with an ammeter in series and a voltmeter in parallel
2. measure the diameter of the wire using a micrometer and calculate its area
3. measure the length of wire used in the circuit
4. measure the current and voltage
5. calculate the resistance of the wire
6. repeat for different lengths
7. plot a graph of R agaisnt 1/L

Question 7

Determine the electrical resistivity of a material control variables

Answer 7

• material of the wire

- power supply

Question 8

Determine the electrical resistivity of a material sources of uncertaintity

Answer 8

• measure diameter of wire (measure at 3 different points +check for zero error first)
• don’t leave power supply on at it heats up and effects equation
• regular resolution uncertainties

Question 9

Determine the electrical resistivity of a material risks

Answer 9

• electricity, check equipment is in good condition

- cut wire, be aware of the sharp wire

Question 10

Determine the emf and internal resistance of an electrical circuit

Answer 10

1. set up a variable resistor, ammeter and switch in series with a voltmeter in parallel over the supply.
2. measure the pd and current for different resistances
3. plot V agaisnt I, the emf is the y intercept and the internal resistance is the gradient

Question 11

emf =

Answer 11

V + Ir

Question 12

Determine the emf and internal resistance of an electrical circuit hazards

Answer 12

• electricity, check equipment is in good condition

- heat/burning, disconnect wire between readings

Question 13

Use a falling ball method to determine the viscosity of a liquid

Answer 13

1. measure the mass of the ball and the volume (measure how much water it displaced) then calculate the density
2. place two rubber bands on the tube which allows for a good time interval of the object moving at terminal velocity
3. drop the ball and measure the time it takes to get from the first band to the second
4. measure the distance between the rubber bands
5. calculate the density of the fluid
6. calculate viscosity using the gathered information

Question 14

How do you measure the volume of an object

Answer 14

measure how much water it displaces

Question 15

Use a falling ball method to determine the viscosity of a liquid control variables

Answer 15

• drop the ball as close to the surface of liquid as possible

Question 16

Viscosity =

Answer 16

(2r^2g(density of ball - density of fluid))/9v

Question 17

Use a falling ball method to determine the viscosity of a liquid sources of uncertaintity

Answer 17

• may be errors in the human reaction time

- uncertaintity due to resolutions

Question 18

Use a falling ball method to determine the viscosity of a liquid risks

Answer 18

• split liquid, clean up spills immediately + keep tube away from the edge
• elastic bands, wear safety goggles + don’t play with the bands

Question 19

Determine the young modulus of a material

Answer 19

1. measure the diameter of the wire. Measure the original length of the wire.
2. attach the wire to the desk and thread it over a pulley with hanging masses on the end. Put a sticky label on the wire at the end of the metre ruler.
3. Add the masses to the hanger and record the distance movement of the sticky marker.
4. plot extension against the weight (mg). The gradient is equal to length/area*young modulus.

Question 20

Determine the young modulus of a material sources of uncertainty

Answer 20

• measure the diameter 3 times and take an average
• measure the masses individually and don’t just use the value given on the mass
• regular resolution uncertainties

Question 21

Determine the young modulus of a material sources of uncertainty risks

Answer 21

• wire under strong force, wear safety goggles and make a paper bridge to go over the wire and absorb the energy from the wire
• hanging masses, mark the area where it falls and avoid it

Question 22

Young modulus =

Answer 22

stress / strain = Fl / Ae

Question 23

Determine the speed of sound in air using a 2-beam oscilloscope, signal generator, speaker and microphone

Answer 23

1. Set up an oscilloscope with a signal generator and speaker a set distance from the microphone.
2. turn the signal generator on. Adjust the oscilloscope to show 3 wave cycles.
3. adjust the spacing between the microphone and the speaker until the waves line up. The measure the distance between.
4. move the speaker until the trace has moved exactly one cycle along and measure this distance.
5. the difference between these distance is the wavelength
6. calculate the frequency by measuring the time period from the trace
7. calculate the velocity by using v = fλ

Question 24

Determine the speed of sound in air using a 2-beam oscilloscope, signal generator, speaker and microphone sources of uncertaintity

Answer 24

• the image on the oscilloscope is likely to be unclear/ rapidly changing leading to a higher uncertaintity
• normal resolution uncertaintities

Question 25

Determine the speed of sound in air using a 2-beam oscilloscope, signal generator, speaker and microphone risks

Answer 25

- high frequency sounds, only leave it one for when it is needed to avoid discomfort - electrical appliances, check its in a condition safe to use

Question 26

Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string or wire method 1

Answer 26

1. Attach a string to a vibration generator and thread it through a bridge and over a pullet with 100g of masses attached to the end 2. turn on the signal generator and vary the frequency until the string oscillates at its fundamental frequency. record this frequency. 3. repeat this for 200g, 300g 400g and 500g 4. calculate the tensions in the string (T = W = mg) 5. calculate how the wave speed changes with different tensions v= √(T/μ)

Question 27

Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string or wire method 2

Answer 27

1. Attach a string to a vibration generator and thread it through a bridge and over a pullet with 100g of masses attached to the end 2. turn on the signal generator and vary the frequency until the string oscillates at its fundamental frequency. record this frequency, record the distance from the signal generator to the bridge. 3. repeat for different lengths between the signal generator and bridge 4. plot a graph of λ agaisnt 1/f the gradient is the wave speed

Question 28

how to calculate mass per unit length

Answer 28

Take 1m of the string and weigh it

Question 29

Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string or wire why different methods

Answer 29

Because its an investigation that finds relationships between a variable and the wave speed

Question 30

Determine the wavelength of light from a laser using a diffraction grating

Answer 30

1. place the laser a measured distance from the wall 2. place the diffraction grating between the wall and laser. 3. mark the points of zero order and first order maxima. measure the distance between n=0 and n=1 4. using the two distances calculate θ using trigonometry 5. using dλ = dsinθ work out λ

Question 31

Determine the wavelength of light from a laser using a diffraction grating sources of uncertaintity

Answer 31

- measure the distance from n=0 to n=1 either side then take an average - regular resolution uncertainties

Question 32

Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string or wire control variables

Answer 32

- when investigating tension keep length constant and vice versa - same type of string

Question 33

Determine the wavelength of light from a laser using a diffraction grating hazards

Answer 33

- lasers, don't shine them into eyes or on reflective - surfaces - electricity, check apparatus is is suitable condition

Question 34

Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string or wire hazards

Answer 34

- hanging masses, mark falling area and don't stand there - wire under tension, wear goggles to protect eyes - electrical equipment, check apparatus is a suitable condition

Question 35

Investigate the relation between the force exerted on an object and its change of momentum

Answer 35

1. set up a trolley attached to masses by a string threaded over a pulley on a tilted ramp. add a light gate near the bottom of the ramp. 2. release the trolly from the top of the slope. Recording the distance to the light gate, the hanging masses, time taken to get to the light gate and the velocity at the light gate. 3. repeat for different masses 4. plot mt agaisnt v. The gradient should equal g. compare the calculated value to the actual value.

Question 36

momentum equation rearrange for question

Answer 36

``` Ft = mv - mu mgt = mv ```

Question 37

Investigate the relation between the force exerted on an object and its change of momentum risks

Answer 37

- hanging masses, keep feet away for falling area | - moving trolley, make sure people are away when youre about to complete the test

Question 38

Investigate the relation between the force exerted on an object and its change of momentum sources of uncertaintity

Answer 38

- human reaction time when timing will cause uncertaintity | - normal resolution uncertainties

Question 39

Investigate the relation between the force exerted on an object and its change of momentum control variables

Answer 39

- angle of slope - distance between release and light gate - trolley mass/ wheel material - string elasticity

Question 40

Investigate the relation between the force exerted on an object and its change of momentum Why make the track a slope?

Answer 40

to counteract the effect of friction

Question 41

Use ICT to analyse collisions between small spheres method

Answer 41

1. measure the mass/diameter of spheres 2. start recording video and roll B into sphere A 3. repeat, varying the lines of approach so that the collision angles are different 4. using tracker software to calculate the momentum before and after the collision

Question 42

Use ICT to analyse collisions between small spheres risk

Answer 42

- fast moving metal spheres could hit and hurt, so don't propell them too fast - getting the camera correct in the set up, could fall and hurt so don't set it up too high

Question 43

Use ICT to analyse collisions between small spheres sources of uncertainty

Answer 43

- can't easily repeat measurements as its hard to achieve the exact same velocity/angle - regular resolution percentage uncertainty

Question 44

Display and analyse the potential differential difference across a capacitor as it discharges through a resistor method

Answer 44

1. set up the circuit above with the first resistor 2. move the switch/flying lead to charge up the capacitor 3. record this pd and V0 4. move the switch for the capacitor to discharge and start the stopwatch 6. record the pd every 10 seconds 7. plot lnV agaisnt t. the gradient is -1/RC and the y intercept is lnV0

Question 45

Display and analyse the potential differential difference across a capacitor as it discharges through a resistor risk

Answer 45

- capacitor retains charge which may cause shocks/electrocution so be sure to discharge - high voltage open circuit could cause shocks so don't let the voltage exceed 40v

Question 46

capacitor discharge equation

Answer 46

V = V0e^-t/RC

Question 47

Display and analyse the potential differential difference across a capacitor as it discharges through a resistor sources of uncertaintity

Answer 47

- human error using a stopwatch | - resolution uncertainties

Question 48

Display and analyse the potential differential difference across a capacitor as it discharges through a resistor controls

Answer 48

- resistance of resistor - capacitance of the capacitor - same wire/ battery

Question 49

Calibrate a thermistor in a potential divider circuit as a thermostat

Answer 49

1. record the temperature of the water 2. put the thermistor in the beaker and record the resistance 3. repeat for a range of temperatures of water 4. plot resistance against temperature then for an unknown temperature record the resistance and read across to find the temperature

Question 50

What type of circuit is used to Display and analyse the potential differential difference across a capacitor as it discharges through a resistor

Answer 50

potential divider circuit

Question 51

Display and analyse the potential differential difference across a capacitor as it discharges through a resistor risks

Answer 51

- water + electricity could result in an electric shock - hot water could scald - glass beaker if broken could cut

Question 52

Display and analyse the potential differential difference across a capacitor as it discharges through a resistor control variables

Answer 52

- same resistor | - same beaker so same surface area of liquid

Question 53

Determine the specific latent heat of ice method

Answer 53

1. measure 50g of ice into the funnel and wait until it reaches 0 degrees 2. record the mass of an empty dry beaker 3. put 100cm^3 of water in the empty beaker and record the total mass m, and the temperature of water 4. add the 0 degrees ice to the water beaker 5. record the lowest temperature reached by the ice/water mixture 6. determine the final total mass of the ice water and beaker 7. Energy received by ice = Energy released by water Lm (of ice) + m (of ice)cΔθ = m(of water)CΔθ

Question 54

Determine the specific latent heat of ice risks

Answer 54

- glass beaker could shatter and cut - melting ice could be a slip hazard - water near electrical equipment

Question 55

Determine the specific latent heat of ice sources of uncertainty

Answer 55

- energy transferred to other places e.g. heat from room | - resolution uncertainties

Question 56

Investigate the relationship between the pressure and volume of a gas at fixed temperature method

Answer 56

either use boyles law equipment or... 1. using a syringe fix a set mass of gas in by sealing off the end. 2. measure the diameter of the syringe in three places, then calculate the area 3. hang masses to change the force, measure the length the syringe increased by each time to get the volume. 4. calculate the pressure 5. plot pressure against 1/volume if its directly proportion it obeys boyles law

Question 57

Investigate the relationship between the pressure and volume of a gas at fixed temperature risk

Answer 57

- high pressure so a safety screen may be neccessary + wear goggles

Question 58

Investigate the relationship between the pressure and volume of a gas at fixed temperature sources of uncertainty

Answer 58

- Atmospheric pressure may effect the graph meaning it won't go through (0,0) - resolution uncertainties

Question 59

Investigate the relationship between the pressure and volume of a gas at fixed temperature control variables

Answer 59

- speed of pumping may cause heating if done too fast

Question 60

Investigate the absorption of gamma rays by lead method

Answer 60

1. measure the width of varying lead sheets using the micrometer 2. record the background radiaion by measuring the counts in 1 minute 3. with each sheet of lead record the counts per minute and subtract the background radiation from it 4. plot width against ln counts the gradient is the decay constant and the y intercept is ln C

Question 61

Investigate the absorption of gamma rays by lead risks

Answer 61

- radioactive material can be bad for health, so point the source away and do not touch - lead can be poisonous if enters the blood stream

Question 62

Investigate the absorption of gamma rays by lead sources of uncertainty

Answer 62

- the further away from the source the less intense the radiation - resolution uncertainties

Question 63

Investigate the absorption of gamma rays by lead control variables

Answer 63

- distance of the source from the lead | - source of radiation (and intensity)

Question 64

Determine the value of an unknown mass using the resonant frequencies of known masses on a spring method

Answer 64

1. record the time for 10 oscillations 2. change the mass and repeat 3. find the time for one oscillation then square it 4. draw a graph of T^2 against mass 5. find the time for an unknown mass then use the graph to determine the mass

Question 65

Determine the value of an unknown mass using the resonant frequencies of known masses on a spring risks

Answer 65

- spring could pin and hit eye so wear goggles | - masses hanging from a stand could fall so clamp to the table

Question 66

Determine the value of an unknown mass using the resonant frequencies of known masses on a spring control variables

Answer 66

- human error so record time for 10 oscillations to reduce - measure masses individually with a top pan balance - resolution uncertainties

Question 67

Determine the value of an unknown mass using the resonant frequencies of known masses on a spring sources of uncertainty

Answer 67

- same spring (so same stiffness)