Ocr Advancing Physics B As - List Of All Practicals You Need To Know

Front 1

Imaging: Describe a polarisation experiment with microwaves.

Back 1

Transmit the microwaves through a metal grille with wires all aligned in one direction. On the other side of the grille have a microwave receiver linked to a voltmeter.

The microwave transmitter transmits polarised microwaves and the intensity of microwaves that pass through the grille will be at a maximum when this axis of polarisation is at right angles to the grille alignment. As the grille rotates to the same alignment as the wave vibration the reading on the voltmeter should decrease.

Front 2

Imaging: Describe an experiment to measure the power of a convex lens:

Back 2

Set up a bulb a set distance away from the lens. eg: u = 0.2m.

Place a screen on the other side of the lens.

Turn on the bulb.

Move the screen in small increments (eg 1cm) until there is a focused image of the filament on the screen.

Measure the image distance and use the equation

1/f -1/u = 1/v to calculate the focal power, f of the lens.

Front 3

Sensing:Describe an experiment to measure the resistivity of a wire:

Back 3

Using a micrometer, measure the diameter of the wire in at least 3 places, and calculate a mean.

One can assume the wire has a circular cross section and so the equation a = π(d/2)^2 can be used.

Clamp the wire to a ruler and connect it to a circuit with a voltmeter in parallel to the wire and an ammeter.

Use a flying lead to only connect a set length of wire and calculate the resistance of the wire at different lengths.

Plot a graph of resistance (y) against length (x) and because the gradient of the line R/L = p/A

multiply the gradient by A to find the resistivity of the wire.

Front 4

Sensing: Describe an experiment to calculate the internal resistance of a cell:

Back 4

Have a circuit with the cell, one variable resistor ,a voltmeter in parallel, and an ammeter in series. It is helpful to have a switch in the circuit.

The resistance can be varied and values on the voltmeter and ammeter recorded for each resistance. Preferably repeat readings at least 2 times for each value of resistance.

Then a graph of voltage (y) and current (x) can be plotted and due to the equation V = -rI + ε the internal resistance of the cell is the negative of the gradient and the e.m.f is the y intercept of the line of best fit of results.

Front 5

Material properties: Describe an experiment to investigate extension by stretching an elastic object such as a spring:

Back 5

Clamp the spring at the top of a clap stand in parallel to a ruler.

Measure the original length of the spring.

Add masses in appropriate increments and record the new length for each length. Calculate the extension for each mass by taking away the value of the original length.

Plot a graph of force (y) and extension (x). The gradient of the graph will be k, the stiffness of the spring. When the limit of proportionality of the spring has been reached, the graph will start to curve.

Front 6

Material properties: Describe an experiment to measure the Young's modulus of a material:

Back 6

Use a micrometer to measure the diameter of the wire in at least 3 places and use the average diameter to calculate a cross sectional area for the wire.

clamp a test wire at one end of a bench and have the wire stretched over a pulley at the edge of the bench.

Mark a point on the wire and measure the distance between the clamped end and the marker. This is the original length.

set up a ruler parallel to the wire from where the marker begins, this will measure extension.

Now add weights to the end of the wire hanging over the edge of of the bench.Measure the extension of the marker each time. Keep increasing the weight until the wire extends plastically and breaks.

Plot a graph of stress (y) against strain (x) and the gradient of the proportional area of the graph is the young's modulus of the material.

Front 7

Waves: Briefly, how can you observe wave interference with sound waves?

Back 7

Use two speakers facing the same way, with a set distance (must be a multiple of λ/2) between them and playing the same sound source.

In front of the speakers moving a microphone across the room you will be able to detect areas of maximum and minimum amplitude.

Front 8

Waves: describe an experiment using standing waves to measure the speed of sound:

Back 8

Apparatus: Tuning fork of known frequency, measuring cylinder,

hollow plastic tube.

Fill the measuring cylinder partly with water, and hold the hollow plastic tube above it so it can move in and out of the measuring cylinder.

Move the hollow plastic tube up and down in the water.Strike the tuning fork at the top of the tube so it resonates.Try to find a point of maximum amplitude.

Measure the distance between the water and the tuning fork at this maximum amplitude, this will be 1/4 wavelength of the sound wave.

Using v = f * wavelength the speed of sound can now be calculated.

Front 9

Waves: How can the refractive index of a glass block be found?

Back 9

Place a glass block on a piece of paper and draw round it.

Use a ray box to shine a beam of light into the glass block. Trace the path of the incoming and outgoing waves.

The block can be removed and the two rays joined to show the path of the ray through the block.

The angles of incidence and refraction can now be measured and used to find the block's refractive index.

Front 10

Waves/quantum: How can you use LEDs to estimate the Planck constant?

Back 10

Connect an LED of known wavelength to a circuit in series with a resistor and high resolution ammeter, and in parallel with a voltmeter. make sure the power source is variable.

Make sure the room is darkened and place a shaded tube over the LED.

Increase the voltage of the power source until the LED just begins to glow. Record the voltage across the LED at this point.

Repeat this for different wavelengths of LEDs.

Plot a graph of voltage(y) against frequency of LED light (x) and the gradient should be h/e.

This is due to the equation eV = hf

Front 11

Describe one experiment to find g using a ball bearing and an automatic timer:

Back 11

Drop a ball bearing from a measured height which breaks contacts to start an automatic timer.

The ball should fall a set distance through a trapdoor which stops the timer.

Repeat 3x for each different height.

On a graph plot height on y and time taken squared on x. The gradient x 2 should be g.

Front 12

How would you use a similar method but with light gates to measure g?

Back 12

Have the ball fall different distances from one light gate to the next.

Plot v^2 - u^2 on y and s on x, and g should be half the gradient.

Front 13

Describe an experiment to find the terminal velocity of a ball bearing falling through a viscous liquid:

Back 13

Put elastic bands at a set spacing on the tube of the liquid, measuring the spacing with a ruler.

Drop the ball bearing in the liquid, and record the time taken for it to fall through each band spacing.

Repeat this a few times and calculate averages for the time taken.

Use the spacing measurement and time taken to calculate average velocity.

The velocities should eventually no longer increase, this is due to the ball reaching terminal velocity.