REQUIRED PRACTICALS

Question 1

how to find the resonance frequency RP1

Answer 1

start by measuring the mass and lengths of string of different types using a mass balance and ruler.
then find the mass per unit length for each string
set up by having a signal generator and vibration transducer on a bench, attached to one side of the string. the string then goes along over a pulley off the bench with mass attached to the other end.
turn on the signal generator and vary the frequency of the vibration transducer.
find the first harmonic
can change length, tension and mass per unit length to see how frequency changes

Question 2

how to set up the young’s modulus double slit experiment RP2

Answer 2

either use two coherent light sources or shine a laser through two slits.
the slits have to be around the same size as the wavelength of the laser light so that its diffracted

Question 3

what will you see on the screen from the double slit experiment

Answer 3

A pattern of light and dark fringes, depending on whether destructive or constructive interference is taking place

Question 4

what would happen if you use white light in the double slit experiment?

Answer 4

the diffraction pattern would be less intense, with a wider maxima. the pattern would also contain different colours with a central wide fringe due to a mixture of frequencies in white light.

Question 5

laser safety precautions

Answer 5

lasers can be very dangerous as laser light is very direct, powerful beam of monochromatic light

to avoid damage:
never shine laser towards a person
wear laser safety goggles
avoid shining laser beam on a reflective surface
turn off laser when not needed

Question 6

what did Youngs double slit experiment show?

Answer 6

that light can have the nature of a wave as it can diffract through two narrow gaps to form an interference pattern.

Question 7

what should you find the relationship between landa and distance to be when investigating diffraction grating interference? RP2

Answer 7

as landa increases so should distance

Question 8

how can you work out the fringe spacing of a certain order maximum? (diffraction grating) RP2

Answer 8

measure using a ruler
by using different laser sources or coloured filters to select certain wavelengths of white light
to you could change the diffraction grating to vary d
or change D by moving observation screen

Question 9

how can you demonstrate a two-source interference pattern? RP2

Answer 9

for water, use one vibrator which drives two dippers
for sound, connect one oscillator to two loudspeakers
for microwaves, attach two microwave transmitter cones to a signal generator.

Question 10

how can you determine g using freefall? RP3

Answer 10

-drop a ball bearing onto a trap door using an electromagnet
-measure the height from the bottom of the ball bearing to the trapdoor
-flick the switch to simultaneously start the timer and disconnect the electromagnetic, releasing the ball bearing
-the ball bearing falls, knocking the trap door down and breaking the circuit which stops the timer
-repeat 3 times and find an average time then repeat but dropping the ball from different heights
-plot a graph h-t^2 to find g

Question 11

what’s the most significant source of error when determining g using freefall?

Answer 11

random error for the value taken for height. uncertainty of the ruler 1mm

and there’s a small systematic error if there’s a delay in the switch or timing mechanism

Question 12

how can you measure internal resistance and emf of a cell or battery? RP6

Answer 12

set up circuit- battery in series with ammeter and voltmeter. variable resistor in parallel with switch.

1.set the variable resistor to the highest resistance
2.close the switch and record the current and pd
3.open the switch and close it again 2 more times to calculate mean current and pd
4.decrease the resistance of the variable resistor and then repeat previous steps with this resistance
5.keep decreasing the resistance till you have 10 readings
6.plot a V-I graph for mean data and draw line of best fit

Question 13

finding the resistivity of a material experiment RP5

Answer 13

1.set up a circuit, power supply connected to an ammeter, the test wire is clamped to a ruler, the other side of the power supply is attached to a switch and a flying lead. voltmeter in parallel
2.calculate the cross sectional area of the test wire using a micrometer
attach the flying lead to the end of the test wire and measure the length of the test wire
3.close the switch and measure current and pd
4.open the switch again and calculate resistance for current and pd
5.repeat this and take a mean
then repeat this at different lengths of wire
6.plot a graph resistance-length and draw line of best fit
7.find resistivity by multiplying gradient by cross-section area of wire

Question 14

investigating the mass-spring system RP7- process

Answer 14

attach a trolley to a spring, pull it to one side by a certain amount then let it go

the trolley will oscillate back and forth as the spring pulls and pushes it in each direction
you can measure the time period by getting a computer to plot a displacement-time graph from a data logger connected to a position sensor

Question 15

what are the three variables you can investigate by using a mass-spring system?

Answer 15

mass, spring content, amplitude

Question 16

mass-spring system with variable as mass experiment RP7

Answer 16

change the mass by loading the trolley with masses
T^2 against mass graph as they should be directly proportional

Question 17

mass-spring system with variable as spring content experiment RP7

Answer 17

change the spring constant by using different combinations of springs
plot a graph T^2 against 1/k as they should be directly proportional

Question 18

mass-spring system with variable as amplitude experiment RP7

Answer 18

change the amplitude by pulling the trolley across by different amounts
plot T against A, T should remain constant as A increases

Question 19

simple pendulum experiment RP7

Answer 19

attach a simple pendulum to an angle sensor and computer
use to computer to plot a displacement time graph and read off time period from this
you can change one variable at a time and see what happens
should show T^2 directly proportional to length

OR

hang the pendulum from a clamp and timing the oscillations using a stopwatch, use a fiducial marker

Question 20

the Youngs modulus experiment RP4

Answer 20

-set up a bench and clamp a wire fixed at one end with a pulley at the other which you will hang weights off
-test wire should be thin and as long as possible
-first find cross sectional area of the wire using a micrometer for the diameter in several places and take an average x pi r^2
-start with the smallest weight necessary to straighten the wire
-measure the distance between the marker and fixed end of wire- this is the un stretched distance
-then increase weight in 100g intervals recording the marker each time to get extension
-then use results to calculate stress and strain and plot a stress-strain graph

Question 21

how to investigate capacitors discharging RP9

Answer 21

-open the switch and remove the power source and add a voltmeter and ammeter and data logger connected to computer
1. close the switch and allow the capacitor to discharge through the resistor
2. when the reading through the ammeter reaches 0, use the computer to calculate the charge on the capacitor over time
3. the computer can then plot a variety of graphs showing how the current, pd and charge vary over time

Question 22

what do the current-time, pd-time and charge-time graphs look like for a capacitor discharging through a fixed resistor?

Answer 22

all decreasing exponentially

Question 23

investigating the inverse square law RP12

Answer 23

-taking measurements of intensity at different distances from a gamma source using a Geiger counter

-set up a Geiger counter connected to a geiger-muller tube with one end at the end of a ruler
-turn on the Geiger counter and take 3 readings then an average for the background radiation
-carefully place the radioactive source at a distance d from the tube
-record the count rate at that distance, take three readings
-move the source so the distance is doubled between it and the tube again take 3 readings
-repeat step 5 for 3d, 4d, 5d …
-once finished, put away radioactive source immediately
-average the count rate for each distance and eliminate background radiation
-plot a graph of corrected count rate- distance of the tube from the source, you should see that as the distance doubles, the corrected count rate will drop to a quarter of its value

Question 24

how to have safe handling of radioactive sources RP12

Answer 24

-always hold a source away from your body when transporting it through the lab
-long handled tongs should be used to minimise the radiation absorbed by the body
-sources of gamma radiation should always be stored in a lead box
-only keep gamma radiation out of the box for the shortest time possible

Question 25

describe an experiment to investigate the effect of current on the force exerted on a current-carrying wire in a magnetic field (RP10)

Answer 25

-set up a top pan balance with a square loop of wire fixed to it, so that it is standing up and that the top of the loop passes through a magnetic field, perpendicular to it

-connect the wire in a circuit with a variable resistor, ammeter and dc power supply. zero the top balance when no current is flowing

-vary the current using the variable resistor. at each current value, record the current and mass. repeat three times and average

-convert into force using F=mg

-plot a graph of force-current and draw line of best fit
gradient is B x length

Question 26

how can you investigate flux linkage with a search coil? RP11

Answer 26

the stretched metal spring acts as a solenoid when connected to an alternating power supply

the alternating supply means the magnetic field of the solenoid is constantly changing- meaning the flux through the search coil is changing which can induce an emf

make sure the peak of the ac voltage from the ac power supply stays the same throughout the experiment

the search coil should have a known area and a set number of loops of fine wire. it’s connected to the oscilloscope to record induced emf in the coil

set up the oscillator so it only shows the amplitude of the emf as a vertical line (turn off base time)

a protractor is used to measure the orientation of the normal to the area of the search coil as an angle from the line of the magnetic field

position the search coil so its about halfway along the solenoid and within the inside of the solenoid but not touching it

then record induced emf in the search coil from the amplitude of the oscilloscope trace

rotate the search coil so its angle to the solenoid and the magnetic flux lines changes by 10 degrees

record the induced emf and repeat until rotated 90 degrees

Question 27

what should happen to the emf as the search coil is turned and why? RP11

Answer 27

as you turn the search coil, emf should decrease
because the search coil is cutting fewer flux lines as the component of the magnetic field perpendicular to the area of the coil gets lower so magnetic flux linkage experienced by the coil is lower
emf should be maximum at 0 degrees
and 0 at 90 degrees

Question 28

how to investigate the relationship between volume and pressure for a fixed mass of gas at constant temperature (Boyles law) RP8

Answer 28

1. set up apparatus- Gordon gauge attached to syringe with vernier calliper and ensure the Hoffman clip is not connected
2. set the plunger so the 20ml syringe contains 10ml of air and seal the end by folding it over and attach the Hoffman clip
3. check the Gordon gauge reads around 1000mbar
4. displace and hold the plunger about 5ml outwards and check the bourdon gauge reading is steady
5. determine the minimum pressure you will be able to reasonably obtain by displacing the plunger outwards
6. record it below along with the starting pressure, 1000mbar, and choose your increment

Question 29

how to investigate the relationship between volume and temperature for a mixed gas at constant pressure (Charles law) RP8

Answer 29

1. set up experiment- tall plastic jug filled with cold water to accelerate cooling, inside put a glass measuring cylinder filled with hot water with a thermometer and stirrer inside and a charles law tube containing a mercury bead- set up with no water initially
2. remove the top from the charles law tube and record initial volume (arbitrary units) and temperature (degree Celsius) of the air column
3. freshly boil the kettle and using a round plastic jug to carry the hot water, carefully fill the measuring cylinder to close to the top
4. wait for the mercury bead to stop rising and record the the volume and temperature of the air column
5. as water cools, record volume is suitable increments of temperature 5 degrees Celsius
6. when the temperature starts to fall more slowly add cold water to accelerate the process and then use ice at around 35 degree c

Question 30

experiment to measure pd across a charging capacitor at regular intervals of time- RP9

Answer 30

• set up circuit, battery connected to resistor and capacitor in series then voltmeter across capacitor and flying lead between capacitor and resistor

-(470x10^-6)F capacitor, fully discharge the capacitor using the flying lead

-after disconnecting the flying lead, record the pd across the capacitor at regular time intervals

-plot voltage-time graph