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# OCR AS Physics Practical Methods

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1. I thought I'd make a thread of most of the AS practicals and the methods for each.

Terminal Velocity:

1) Get a vertical tube, and fill it with a viscious liquid. (e.g. wallpaper paste).

2) Using a metre ruler, mark regular. consecutive intervals using tape or a rubber band. For example, mark every 10cm on the tube.

3) Drop a ball bearing into the tube, and using a timer, record the time taken for the ball bearing to reach each individual interval.

4) Repeat this several times (at least 3) and use these to calculate an average value for the time taken.

Using these average values, you can calculate the velocity (distance of each interval/time taken).

5) Plot this on a velocity x time graph and draw a line of best fit (which is representative of the acceleration).

You should observe a linear section, and then it eases off into a straight line. Where the linear section ends and flattens out, is the terminal velocity.
2. Young Modulus:

1) Using a micrometer, measure the diameter of the wire in several places and find an average (this is done to find the cross sectional area)

2) Clamp the wire down horizontally, with it hanging over a pulley on one side, with a ruler reading 0cm at the clamp.

3) Using the ruler (metre ruler), mark the wire at a specific place and read the initial length.

3) Add a mass of known weight (1N or 2N), and then measure the length again from the clamp to where the marker on the wire has now moved. You can find the extension by doing new length - original.

4) Repeat this, with increasing the weight hanging over the end of the wire.

5) You can use this data to find the stress and strain using the formulas, and then plot a graph of stress against strain. The gradient of this line is equal to the Young Modulus -- but only the LINEAR section of the line of best fit.

Feel free to contribute and ask questions
3. Hooke's Law:

1) Hang the test wire vertically on a clamp, against a ruler so you can measure it with ease.

2) Measure the origin vertical length when there is no mass attacked to it.

3) Add a mass of known weight, regularly, measuring the new length of the test wire.

4) Record this data and use it to plot a graph of force (weight of mass) and the corresponding extension.

If the line of best fit is linear, then the material is said to obey Hooke's Law.
4. Acceleration of freefall:

1) Take the object, and measure the height from which it will be dropped using a metre ruler.

2) Using a timer measure the time taken for the object to fall and land at the bottom of the measured distance (e.g. from 1m to the ground).

3) Repeat this several times to get a more accurate measure as there is a large uncertainty due to human reaction time.

4) Use the time and distance to calculate an AVERAGE value of g:

s = ut + 1/2(at^2)

Initial velocity is 0 therefore this becomes:
s = 1/2(at^2)

Rearrange for a:
2s/t^2 = a

To improve accuracy, ou could use lightgates which will provide very accurate readings for time, thus eliminating the largest cause of error -- human reaction time.

Also, this is an average value as there is air resistance, however we are ignoring it so this value deviates from the actual value of 9.81.
5. Are there any others apart from this that we need to know for module 4 topics?

Thanks by the way, really helpful!
6. (Original post by Turtlebunny)
Are there any others apart from this that we need to know for module 4 topics?

Thanks by the way, really helpful!
Yeah, I think there are quite a few to remember but I havnt gotten the chance to go through them all. I will hopefully post them as soon as I do though.
7. Could you put some up for Standing Waves/Polaroids/Diffraction Gratings/Photoelectric1&2? But thanks for these - very useful =)
9. (Original post by voltz)
Acceleration of freefall:

1) Take the object, and measure the height from which it will be dropped using a metre ruler.

2) Using a timer measure the time taken for the object to fall and land at the bottom of the measured distance (e.g. from 1m to the ground).

3) Repeat this several times to get a more accurate measure as there is a large uncertainty due to human reaction time.

4) Use the time and distance to calculate an AVERAGE value of g:

s = ut + 1/2(at^2)

Initial velocity is 0 therefore this becomes:
s = 1/2(at^2)

Rearrange for a:
2s/t^2 = a

To improve accuracy, ou could use lightgates which will provide very accurate readings for time, thus eliminating the largest cause of error -- human reaction time.

Also, this is an average value as there is air resistance, however we are ignoring it so this value deviates from the actual value of 9.81.
An alternative to this method would be using an electromagnet and trapdoor.

A steel ball is held by an electromagnet when the current is turned on. Before you start, you would need to measure the distance between the ball and trapdoor. You would then switch the current off, causing the electromagnet to demagnetise and cause the ball to drop. As soon as you switch the current off, a timer is triggered which means no human error is involved. The ball drops through the distance in a fixed time, hits the trapdoor and causes a break to be made in the circuit. This break turns off the timer and so you use the equation done above to work out the value of g.

I don't know if this is even helpful but meh. Should I post other practicals too or do you want to cover them here yourself?
10. (Original post by M0nkey Thunder)
An alternative to this method would be using an electromagnet and trapdoor.

A steel ball is held by an electromagnet when the current is turned on. Before you start, you would need to measure the distance between the ball and trapdoor. You would then switch the current off, causing the electromagnet to demagnetise and cause the ball to drop. As soon as you switch the current off, a timer is triggered which means no human error is involved. The ball drops through the distance in a fixed time, hits the trapdoor and causes a break to be made in the circuit. This break turns off the timer and so you use the equation done above to work out the value of g.

I don't know if this is even helpful but meh. Should I post other practicals too or do you want to cover them here yourself?
11. You are the best
12. (Original post by M0nkey Thunder)
An alternative to this method would be using an electromagnet and trapdoor.

A steel ball is held by an electromagnet when the current is turned on. Before you start, you would need to measure the distance between the ball and trapdoor. You would then switch the current off, causing the electromagnet to demagnetise and cause the ball to drop. As soon as you switch the current off, a timer is triggered which means no human error is involved. The ball drops through the distance in a fixed time, hits the trapdoor and causes a break to be made in the circuit. This break turns off the timer and so you use the equation done above to work out the value of g.

I don't know if this is even helpful but meh. Should I post other practicals too or do you want to cover them here yourself?
Thanks, and more if you want, contribute as much as you wish
13. Standing Waves:

This is done by confining a wave between two media, e.g. a string between two pulleys.

1) A progressive wave is formed at one end of the string, this can be done by plucking the string or using an ocsillator.

2) The wave travels away from the source and towards the other end and is reflected off the pulley, so travelling back towards its source.

3) Here, it interferes with progressive waves which are coming from the source (oscillator etc).

4) The two progressive waves which are travelling in opposite directions interfere and form standing waves with nodes and antinodes.

5) Constructive interference produces antinodes - regions of maximum oscialltion.
Destructive interference produces nodes - regions of minimum/zero oscillation.

This can be applied to any context, e.g. how standing waves are formed when microwves are emitted into a small cubes, the same principles apply as they intefere etc
14. Planck Constant:

This experiment will require a cell, ammeter, voltmeter, resistor and LED lights of varying colours/wavelengths.

1) Attach an LED to the circuit using a flying lead to complete the circuit, and start with the resistor on maximum resistance.

2) Using some sort of tube, look at the light on the LED to see when the LED first starts to emit light. Simultaneously, turn the resistor down very slowly.

3) When the light first begins to be emitted, record the corresponding voltage and current for that wavelength. This is the "threshold frequency".

4) Repeat this fro LEDs with varying wavelengths.

5) Use the data recorded to plot a graph of Voltage (threshold) no the y-axis and 1/wavelength on the x axis.

The gradient of the graph is equal to V/Wavlength, since V = eV, we can rearrange this:

eV = hc/wavlength
V = hc/ wavelength*e

Now rearrange into the form y = mx + c:

V = hc/e * 1/wavelength

So using the graph we can calculate the planck constant (estimate):

Planck constant = gradient * 1/wavelength
15. Polaroids:

This is a method to check if a wave is plane polarised:

1) Set up the source around 1 meter from a detector. In this example we'll use microwaves so set up the microwave transmitter opposite the detector which will be connected to a meter which will show the intensity of microwaves deteccted.

2) Hold a diffraction grating between the the detector and emitter. The reading on the detector should be at a maximum, showing that the wave is travelling through the diffraction grating.

3) Slowly rotate the diffraction grating through 90 degrees. You should observe that the intensity decreases as it is rotated, as the wave can no longer travel through the diffractoin grating. This shows the the wave is polarised perpendicular to the direction of the grating slits.

4) As you rotate it again through every 90 degrees, you should see the intensity increase and decrease. At 360 degrees, you will observe the original reading.

5) This shows that the wave is plane polarised, and the vibrations are in 90 degrees to the direction of energy transfer -- confined to the plane of the diffraction grating when the detector reading is at a maximum.

Same idea applied to polaroids, where the polaroid absorbs the light if the slit is perpendicular to plane polarised wave.
16. (Original post by voltz)
Planck Constant:

This experiment will require a cell, ammeter, voltmeter, resistor and LED lights of varying colours/wavelengths.

1) Attach an LED to the circuit using a flying lead to complete the circuit, and start with the resistor on maximum resistance.

2) Using some sort of tube, look at the light on the LED to see when the LED first starts to emit light. Simultaneously, turn the resistor down very slowly.

3) When the light first begins to be emitted, record the corresponding voltage and current for that wavelength. This is the "threshold frequency".

4) Repeat this fro LEDs with varying wavelengths.

5) Use the data recorded to plot a graph of Voltage (threshold) no the y-axis and 1/wavelength on the x axis.

The gradient of the graph is equal to V/Wavlength, since V = eV, we can rearrange this:

eV = hc/wavlength
V = hc/ wavelength*e

Now rearrange into the form y = mx + c:

V = hc/e * 1/wavelength

So using the graph we can calculate the planck constant (estimate):

Planck constant = gradient * 1/wavelength
do you know how to draw a diagram for this? I can't find a simple one
17. (Original post by Inker)
do you know how to draw a diagram for this? I can't find a simple one

I drew a *****y one in paint for you but you should get the idea

edit: also i can do some write ups on experiments if anyone wants me to. I'm on OCR B so I might not know all the A ones. i guess its good revision for me!
18. Ahah I'm on OCR B too, please please write up some experiments😊
19. (Original post by dfbenjamin)

I drew a *****y one in paint for you but you should get the idea

edit: also i can do some write ups on experiments if anyone wants me to. I'm on OCR B so I might not know all the A ones. i guess its good revision for me!
thanks so much, that looks perfect!
20. I cant think of any more practicals, but if there are more please let me know and I will try my best to post a method

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