PAGs Flashcards
Equipment when using light gates to compare g
Clamp stand
Equipment connected to low-voltage DC supply
Steel ball bearing
Data Logger
Metre Ruler
2kg Counterweight
Soft pad for the ball bearing to land on
Method when using light gates to compare g values
Use a clamp stand to clamp the electromagnet which is connected to a low-voltage DC supply and the 2kg counterweight beside the bottom of the clamp
Connect the light gates to a data logger and as close to the electromagnet as possible and the pad below the light gates
The position of the lower light gate should be 0.75m above the floor measured using a metre ruler
Turn on the electromagnet and attach the ball bearing
Switch off the electromagnet and note the time taken for the bearing to fall between the light gates as recorded by the data logger
Reduce by 0.05m by moving the light gate upwards and repeat the process and reducing h by 0.05m until h = 0.25m
Repeat the whole experiment twice more to find mean values of t for each value of h
Calculations for using a light gate to compare g values
Plot a graph of 2h against t^2 and draw a line of best fit
The gradient will be g and can be derived using suvat
Notes for using light gates to compare values for g
The ball bearing should be dense to mitigate the effects of air resistance
Distance between the upper right gate and the starting position of the ball must be kept constant
Ruler can be clamped next to light gates to reduce parallax error
Equipment when investigating terminal velocity
Long plastic tube
Elastic band
Ruler
Clear viscous fluid
Steel ball bearing
Stopwatch
Strong magnet
Method when investigating terminal velocity
Wrap elastic bands around the tube of viscous liquid at set intervals measured by the ruler
Drop the ball into the tube and record the time it reaches each band
Repeat 4 times to reduce the effect of random errors and use the strong magnet to remove the ball bearing from the bottom of the tube
Calculations when investigating terminal velocity
Calculate time taken to travel between consecutive bands and calculate the average of this time for each experiment
Use the equation speed = distance/time to find the average velocity of the bearing between each set of bands
Plot a graph of velocity against time - velocity the graph tends to is the terminal velocity
Notes when investigating terminal velocity
Using a taller tube allows the bearing to travel at its terminal velocity for longer
Using larger intervals for the bands reduces the percentage uncertainty in both the distance and time between the bands
0 resultant force on the bearing
Equipment when investigating initial speed and stopping distance
Metre ruler
Wooden Blocks
Light Gate
Interruptor card
Method when investigating initial speed and stopping distance
A vehicle is modelled by the block of wood which is pushed and decelerates due to friction with the surface it moves on
Glue the interrupter card to the side of the block of wood so that the time for the width of the card to pass through the gate is recorded - the interrupter card allows the distance moved through the light gate to be fixed as it registers with the light gate easily without the light gate interrupting the block’s motion
Set up the light gate such that it records the average starting velocity of the block moving through it
Record the starting position of the block and position the light gate 2cm after this point
Push the block and record the position at which it stops
Record the average starting velocity and the corresponding distance between the light gate and the stopping point in a table
Notes when investigating initial speed and stopping distance
The surface the block is pushed on and the block material should stay constant so that the frictional force varies as little as possible
Estimate Planck’s Constant using LEDs
Diodes only allow forward current flow once a threshold p.d is applied across them
After that point, an LED will allow current to flow and transfer energy to EM radiation/photons of a specific wavelength
At the threshold p.d - it may be assumed the energy of a single electron is transferred completely to the energy of a single photon, of a given frequency/wave
A single value of h can be obtained from a single LED
Plot a graph of V against 1/lambda where gradient = hc/e
