Experiments Flashcards
1
Q
Measuring g (by using an object in free fall)
A
- Measure the height h from the bottom of the ball bearing to the trapdoor.
- Flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing.
- The ball bearing falls, knocking the trapdoor down and breaking the circuit-which stops the timer.
- Use the time t measured by the timer, and the height h that the ball bearing has fallen, to calculate a value for g, using h= 1/2 x g x t^2
- Most significant error in this experiment will be in the measurement of h. Using a ruler, you’ll have an uncertainty of about 1 mm.
2
Q
How to investigate the distance a trolley has rolled affects its speed.
A
- Measure length of the trolley.
- Make a start line on the ramp to make sure the trolley always starts from the same position.
- Measure the angle of the ramp, and the distance from the chosen start line to the light gate, d.
- Place the trolley on the ramp and line it up with the start line. Let go of it so its initial velocity, u, is 0.
- The data logger will record the time taken for the trolley to pass through the light gate and calculate the velocity of the trolley as it passes through the gate.
- Change the starting position of the trolley, so d is varied.
- Repeat this experiment for each distance 3 times and average the recorded velocities to reduce the error in you final result.
3
Q
You can find the centre of mass in a regular shape by…
A
symmetry.
4
Q
Experiment to find the Centre of Mass of an irregular object.
A
- Hang the object freely from a point (e.g. one corner)
- Draw a vertical line downwards from the point of suspension- use a plumb bob to get your line exactly vertical.
- Hang the object from a different point.
- Draw another vertical line down.
- The centre of mass is where the two lines cross.
5
Q
Measure the Terminal Velocity of a Ball Bearing
A
- Put elastic bands around a tube of viscous liquid at fixed distances using a ruler.
- Drop a ball bearing into the tube, and use a stopwatch to record the time at which it reaches each band. Record your results in a table.
- Repeat this a few times to reduce the effect of random errors on your results. You can use a strong magnet to remove ball bearing from the tube.
- Calculate the times taken by the ball bearing to travel between consecutive elastic bands and calculate an average for each reading. Use the average times and distance between bands to calculate the average velocity between each pair of elastic bands.
- You should find that the average velocity increases at first, then stays constant- this is the ball bearing’s terminal velocity in the viscous liquid used.
6
Q
Investigate extension of a spring.
A
- Apparatus: spring, clamp, ruler, spring, weights, clamp stand.
- Measure springs original length
- Add weights one at a time to the bottom of the object.
- After each weight is added, measure the new length of the object, then calculate extension (x= new l- original l)
- Plot a graph of force against extension for your results. Where the line of best fit is straight, then Hooke’s law is obeyed, and the gradient k (force constant f=kx)
- If you have loaded the object beyond its limit of proportionality, the graph will start to curve.
- Safety: stand out of way where weights could fall, wear goggles incase spring breaks.
7
Q
To find Young Modulus
A
- Test wire should be thin, and as long as possible. The longer and thinner the wire, the more it extends for the same force. This reduces the uncertainty in your measurements.
- Find CSA of the wire. Use a micrometer to measure the diameter of the wire in several places and take average of your measurements. The find CSA by PIE x r^2
-Clamp the wire to the bench so you can hang weights off one end of it. Start with the smallest weight necessary to straighten the wire.
-Measure the distance between the fixed end of the wire and the marker- this is you unstretched length. - Increase the weight in steps (e.g. 1N), recording the marker reading each time- the extension is the difference between this reading and the unstretched length. Use a mass meter or a set of digital scales to accurately find the weight you add at each step.
- You van use your results from this experiment to calculate stress and strain on the wire and plot a stress-strain graph.
YM= gradient
8
Q
Investigate the resistivity of a wire.
A
- Find CSA of wire using micrometer.
- Test wire should be clamped to a ruler and connected to the rest of the circuit at the point where the ruler reads zero.
- Attach the flying lead to the test wire- the lead is just a wire with a crocodile clip at the end to allow connection to any point along the test wire.
- Record the length of the test wire connected in the circuit the voltmeter reading and the ammeter reading
- Use your readings to calculate the resistance of the length of wire using R= V/I
- Plot resistance against length and draw a line of best fit
- grad= (R/L)= (row/A) so multiply gradient by CSA.
- Resistivity of a material depends on its temperature, so you can only find the resistivity of a material at a certain temp.
9
Q
Investigate the I-V characteristics of a component.
A
- Use a variable resistor to alter the pd across the component and the current flowing through it, record V and I
- Repeat your measurements and take averages to reduce the effect of random error.
- Plot a graph of current against pd from your results. This graph is the I-V characteristics of the component and you can use it to see how resistance changes.
10
Q
Investigating Polarisation of light using two polarising filters.
A
- Align the transmission axes of two polarising filters so they are both vertical. Shine unpolarised light on the first filter. Keep the position of the first filter fixed and rotate the second one.
- Light that passes through the first filter will always be vertically polarised.
- When the transmission axes of the two filters are aligned, all of the light passes through the first filter also passes through the second.
- As you rotate the second filter, the amount of light that passes through the second filter varies.
- As the second filter is rotated, less light will get through it as the vertical component of the second filter’s transmission axis decreases. This means the intensity of the light getting through the second filter will gradually decrease.
- When the two transmission axes are at 45 degrees to each other, the intensity will be half that getting through the first filter. When they are at right angles (90 degrees) to each other no light will pass through- intensity is 0.
- As you continue turning the intensity should begin to increase once again.
- When the two axes realign (after 180 degrees), all the light will be able to pass through the second filter again.
11
Q
Polarising Microwaves using a metal grille.
A
- Place a metal grille between the microwave transmitter and receiver.
- The intensity of the microwaves passing through the grille is at maximum when the direction of vibration of the microwaves and the wires on the grille are at right angles to each other.
- As you rotate the grille, the intensity of the polarised microwaves able to pass through the grille decreases, so the reading on the voltmeter decreases.
- When the wires on the metal grille are aligned with the direction of the polarised waves, no signal will be shown on the voltmeter.
12
Q
You can use a ripple tank to investigate diffraction.
A
- Ripple tanks are shallow tanks of water that you can generate a wave in.
- This is done by an oscillating paddle, which continually dips into the water and creates regular waves with straight, parallel wave fronts.
- Objects are then placed into the ripple tank to create a barrier with a gap in the middle of it.
- This gap can be varied to see the effects this has on how the waves spread through the tank.
- When gap is a lot bigger then wavelength diffraction is unnoticeable.
- As gap smaller more diffraction
- Max diffraction when gap as wide as wavelength.
13
Q
Demonstrate Diffraction in light by using laser light.
A
- Diffraction in light can be demonstrated by shining a laser light through a very narrow slit onto a screen. You can alter the amount of diffraction by changing the width of the slit.
- You can do a similar experiment using a white light source instead of the laser and set color filters. The size of the slit can be kept constant while the wavelength is varied by putting different colour filters over the slit.
14
Q
Investigating refraction
A
- Place a glass block on a piece of paper and draw around it.
- Use the ray box to shine a beam of light into the glass block. Turn off any other lights so you can see the path of the light beam through the block clearly.
- Trace the path of the incoming and outgoing beams of light either side of the block.
- Remove the block and join up the two paths you’ve drawn with a straight line that follows the path the light beam took through the glass block. You should be able to see from drawing how the path of the ray bent when entering and leaving the block.
- Measure the angles of incidence, and refraction where the light enters and exits the block. Air is less optically dense than glass, so the light enters the glass block it bends towards the normal (angle of incidence > angle of refraction) as it slows down. The beam should bend away from the normal as it exits the block (angle of refraction < angle of incidence) and speeds up.
15
Q
Investigating Critical angles and Total Internal Reflection with Glass Blocks.
A
- Shine a light ray into the curved face of a semi-circular glass block so that it always enters at right angles to the edge- this means the ray won’t refract as it enters the block, just when it leaves from the straight edge.
- Vary the angle of incidence, until the light beam refracts so much that it exits the block along the straight edge. This angle of incidence is the critical angle, C, for glass-air boundary.
- If you increase the angle of incidence so it’s greater than C, you’ll find the ray is reflected from the straight edge block.
- Angle of incidence less then critical angle- some beam refracted, partially reflected.
- Angle of incidence equal to C- refracted along boundary, stronger reflected ray.
- Angle of incidence greater than C- TIR
