Physics Experiments on Falling Objects and Resistivity

1. Open switch to break connections between battery and electromagnet in the primary circuit and turn on the timer in the secondary circuit
2. Electromagnet demagnetises causing steel ball to fall a distance, h, from the bottom of the ball to the top of the trap door, measure h with a ruler
3. When the ball falls through the trap door it stops the timer
4. Record the time taken to fall h, repeat process three times, discard anomalies and find average time
5. Vary h and record corresponding t

s= h u=0 a=g t=t

using s=ut+0.5at^2

t^2 = 2/g * h

plot t^2 against h and draw a line of best fit

g = 2/m

If dropping of a table, clamp electromagnet stand to table to prevent it toppling over be aware of falling ball, use a tray to capture ball at bottom small currents used in circuit, no danger of electric shock

small t values, use a larger distance to reduce uncertainty time delay between the timer starting and ball being released due to residual magnetism in ball, use a lower current so that the electromagnet has a weaker magnetic feild Air resistance, use a smaller heavier ball so travels faster.

1. At various points along the wire measure the diameter, d, repeat at 90 degree angles at the same point get about 6 readings and find average, and calculate the cross-sectional area, A,
2. Connect circuit shown above
3. At 10 cm intervals from the crocodile clips, touch wire with probe, record voltage,v, and current, I, readings on Voltmeter and ammeter
4. Calculate resistance R as V/I
5. Measure length of wire,L , from one crocodile clip along the wire and record coresponding values of R

Plot R against L and draw line of best fit with eqaution

R = p/A * L

calculate the resistivity

p = gradient * A

small voltage used so little danger of electric shock wire may get warm so dont touch unless with probe

If there is a highly varying volatage/ current readings, remove power supply, voltmeter, ammeter and replace with ohm meter (connect clips/probe directly to it ) Uncertainty from micrometre is doubled as radius is sqaured Poor connection between crocodile clips and wire means a higher resistance is measured Use ohm meter to achieve resistance directly, reduce the wire heating (uses a very low current ) Avoid pressing too hard on wire as deformation affects cross sectional area and resistance Ensure wire is straight so length measurement is accurate

1. Set up the apparatus as shown in the diagram
2. Measure the PD across the terminals Vt using voltmeter
3. Vary current in circuit by changing value of load resistance, R using variable resistor, measure pd for several values of I
4. Repeat several times and find average Vt and I

Plot graph of Vt against I, draw line of best fit with eqaution

Vt = ℰ - Ir

graident is negative internal resistance -r Y intercept is ℰ

low pd so no danger of shock variable resistor may get hot so handle with care

Keep temperature constant by opening switch between readings to prevent current flow in between each trail Could use a multimeter as it is difficult to read meters simultaneusly when there are fluctuating readings on the meters

1. Zero a mass balance with a 250 cm3 measuring cylinder on top
2. Pour washing up liquid up to the 200 cm3 mark, record the mass and determine the density of the liquid
3. measure the mass of the ball bearing using a top pan balance
4. Measure diameter of the ball bearing with mirco meter(different positions and take average ), then calculate the volume of the ball
5. Calculate the density of the ball bearing
6. Place elastic bands along the measuring cylinder 10cm apart, measured with a ruler
7. Drop the ball into the cylinder
8. Start the stop watch when the ball touches the top of the washing up liquid, lap when the bottom of the ball just passes a rubber band
9. Record these 2 times t1 and t2
10. Repeat two more times with same radius sphere, and then with same mass but varying radii
11. For each radius find average t1 and t2, calculate velocities v1 and v2 and average to find V avg for each radius

For each radius where ps is density of ball bearing and pl is density of liquid find the viscosity n

n= 2(ps - pl)g / 9v avg

average the viscosity values to find mean viscosity

Spilled liquid can make it easier to slip, so mop up spills use gloves if allergic to liquid wear goggles to avoid splaches in eye

Keep temp roughly the same as it may change the viscosity of the liquid Ensure the lap timer is hit for constant paorts of the ball larger distance between the elastic bands will lower the percentage uncertainty, but there will still be a high uncertainty in time due to human error light gates and data loggers can be used to eliminate uncertainty due to reaction time If ball falls close to wall repeat and flow wont be laminar If velocity at second band is higher than the first band, ball bearing might not have reached terminal velocity, when you started timing, so move bands futher down and try again

1. Set time base on oscilloscope to 100ms/cm, and y-gain 0.1 volts/cm
2. Connect microphone to input on oscilloscope, activate second beam mode
3. Place microphone in front of speaker and set signal generator to 1000Hz
4. Place a metre ruler between the signal generator and microphone
5. Move the microphone away from the loudspeaker, until the microphones wave has moved one full wavelength along the signal generators wave, so the peak and troughs line up
6. Measure the distance using the metre ruler as one wavelength
7. Keep moving microphone back and recording the distance at which the traces line up until 1 metre is reached
8. Convert the measured distances so as to record the length of one complete wavelength For 2nd result divide length by 2 For 3rd result divide length by 3 etc
9. Find the mean wavelength
10. On the oscilloscope, find the time period (number od squares for 1 wavelength * timebase ), then invert to find actual frequency being produced
11. Vary the frequency on the signal generator to 2000Hz and 3000Hz and repeat procedure as above
12. Calculate the speed of sound at each frequency using v = f * wavelength, and then calculate the mean speed of sound

Hearing protection used as high frequency sound can be painful to listen to for long period of time sound not too loud to avoid ear damage

Changing the timebase until only 1 wavelength is shown, reduces uncertaintiy in measurements finding the frequency from the oscilloscope overcomes uncertainties in the signal generator make sure oscilloscope dial is in calibrate position The tiem interval is very small, so maximise the distance between microphones

1. measure the mass and length of the strinf between the transducer and the pulley using a metre ruler and a mass balance
2. Caluclate themass per unit length, mu mu = mass of string / length of string
3. keep 10g of mass on the end of the pulley to keep tension constant, and the length of the string constant
4. Change the strings mass per unit length by using a thicker string of different material
5. Plot frequency against mu and draw line of best fit to determine the relationship between the two variables

1. measure the length of the string between the transducer and pulley using a metre ruler
2. Keep 10g of mass on the end of the pulley to keep the tension constant
3. change the length of the string between pulley and transducer, use the same string to keep mu constant
4. Record and plot fundamental frequency against length to find the effect of length on fundemental frequency

no major hazards- string is elatic so won't snap easily, low masses used, pulley firmly attached to bench

using oscilloscpe overcomes uncertainty in signal generator Dont use heavier masses, in order to keep low frequencies required to form the first harmonic Set timebase on oscilloscope so one wavelength is on the display, to reduce uncertainty in measuring the distance across timebase

1. Shine mono chromatic light (same wavelength) through 2 slits and to produce 2 coherent wave sources
2. The coherent waves will interfere as they overlap Points of contrctive interfernce form bright fringes on the screen Points of destructive interference form dark fringes on the screen
3. Measure the slit to screen distance, D in metres
4. Measure the slit distance, a in metres
5. Measure the fringe seperation, x
6. Calculate the wavelength as followed

wavelength = ax/ D

if you use 2 sources the two waves will not be coherent Slits be small enough to cause diffraction of light and close enough to allow interference

1. Record the masses, m of two spheres using a mass balance then place them on a level table top
2. Postion two metre rulers perependicular to each other using a set square
3. Position a video camera above the table top, and start camera recording
4. Roll one sphere towards stationary sphere and allow them to collide and roll
5. Stop recording when both spheres come to rest
6. Use video analysis software to go through each frame of the video, use the rulers to calculate the distance travelled and calculate the time between each frame
7. Use compents to find intital and final velocity of the spheres
8. Use velocities to show momentum is conserved

Uncertainty in velocities comes from half the range of repeat readings Friction cannot be accounted for in 2D

For Charging

1. Set up a circuit with a DC power supply, high resistance resistor
2. Close switch to charging position and start the timer
3. Record PD and current every 10s
4. Repeat process 3 times and calulate mean V and I
5. Plot graph of current against time and PD against time For discharging same method jsut move switch to discharging postion

Ensure that the capacitor is connected the right way, as to prevent it exploding Use low (sub 40 V ) voltages for open circuit work

Increasing the circuit resitance causes the capacitor to discharge slower, measuring a larger value for time reduces percentage uncertaintity(and effect of reaction time)

Thermistor is R1

Boiling water/ busen burner includes a risk of scalds and burns so dont handle the beaker when hot dont exceed the voltage limit of the thermistor keeps leads away from hot things to prevent melting the plastic coating Support the thermistor to prevent it tipping the beaker over

Measure the mass and length of the string between the transducer and pulley using a metre ruler and a mass balance Calculate themass per unit length, mu mu = mass of string / length of string Keep 10g of mass on the end of the pulley to keep tension constant, and the length of the string constant
Change the strings mass per unit length by using a thicker string of different material Plot frequency against mu and draw line of best fit to determine the relationship between the two variables

Measure the length of the string between the transducer and pulley using a metre ruler Keep 10g of mass on the end of the pulley to keep the tension constant Change the length of the string between pulley and transducer, use the same string to keep mu constant Record and plot fundamental frequency against length to find the effect of length on fundemental frequency

no major hazards- string is elatic so won't snap easily, low masses used, pulley firmly attached to bench

using oscilloscpe overcomes uncertainty in signal generator Dont use heavier masses, in order to keep low frequencies required to form the first harmonic Set timebase on oscilloscope so one wavelength is on the display, to reduce uncertainty in measuring the distance across timebase

1. Shine mono chromatic light (same wavelength) through 2 slits and to produce 2 coherent wave sources
2. The coherent waves will interfere as they overlap Points of contrctive interfernce form bright fringes on the screen Points of destructive interference form dark fringes on the screen
3. Measure the slit to screen distance, D in metres
4. Measure the slit distance, a in metres
5. Measure the fringe seperation, x
6. Calculate the wavelength as followed

wavelength = ax/ D

if you use 2 sources the two waves will not be coherent Slits be small enough to cause diffraction of light and close enough to allow interference

1. Record the masses, m of two spheres using a mass balance then place them on a level table top
2. Postion two metre rulers perependicular to each other using a set square
3. Position a video camera above the table top, and start camera recording
4. Roll one sphere towards stationary sphere and allow them to collide and roll
5. Stop recording when both spheres come to rest
6. Use video analysis software to go through each frame of the video, use the rulers to calculate the distance travelled and calculate the time between each frame
7. Use compents to find intital and final velocity of the spheres
8. Use velocities to show momentum is conserved

Uncertainty in velocities comes from half the range of repeat readings Friction cannot be accounted for in 2D

For Charging

1. Set up a circuit with a DC power supply, high resistance resistor
2. Close switch to charging position and start the timer
3. Record PD and current every 10s
4. Repeat process 3 times and calulate mean V and I
5. Plot graph of current against time and PD against time For discharging same method jsut move switch to discharging postion

Ensure that the capacitor is connected the right way, as to prevent it exploding Use low (sub 40 V ) voltages for open circuit work

Increasing the circuit resitance causes the capacitor to discharge slower, measuring a larger value for time reduces percentage uncertaintity(and effect of reaction time)