Practical

Question 1

Photogates + Electronic timer

Answer 1

The object is projected so that it passes through the two pairs of photogates. Record the timings at which it passes both gates as t1 and t2. Calculate the time taken for the object to pass through the photogates using Δt = t1 - t2.

Measure the distance between the photogates using a ruler and record as x.

Calculate the velocity of the object using v = x / t and record as v.

Question 2

Stroboscope

Answer 2

Starting with the highest available frequency, the frequency of the strobing is gradually reduced until the vibrating object appears stationary. This means that the frequency of strobing is equal to the frequency of vibration of object.

Question 3

Spectrometer

Answer 3

Place the diffraction grating on the platform of a spectrometer. Use the telescope to locate the positions of the maxima and use the scale of the spectrometer to find the angle of deviation of the beam.

Question 4

Cathode Ray Oscilloscope (CRO)

Answer 4

Connect a CRO in parallel to the ___. Adjust the time-base/Y-scale on the C.R.O. to maximise the waveform on the C.R.O. display. Using the grid on the screen, measure the horizontal/vertical distance occupied by one complete waveform. Multiply this distance by the time-base scale/Y-scale indicated to obtain the time interval/peak-to-peak (voltage).

Question 5

Temperature sensor connected to datalogger

Answer 5

Place the temperature sensor in the ___ Connect the termperature sensor to a datalogger and computer to generate a graph of temperature against time.

Constant temperature environment can be set up using a sand bath or water bath. Enclose the object if exposed to air to prevent convection current.

Question 6

Hall probe

Answer 6

The hall probe must be positioned so that the magnetic field are at right angles to the plane of the Hall probe. The probe should be calibrated using a magnetic field of known strength. The magnetic field strength is assumed to be proportional to the voltmeter in the meter.

Question 7

Geiger Muller counter

Answer 7

Use the GM tube to measure the background count rate of the environment.
Use the GM tube to measure the count rate of the radiation emitted by the source. Difference of the two count rate is the actual count rate of the source.

Question 8

Intensity meter with sensor

Answer 8

The sensor should be positioned such that it is perpendicular to the direction of the light.

Question 9

How to enhance accuracy and reduce errors

Answer 9

1. Use of additional apparatus to ensure higher precision or accuracy. (e.g. set square, spirit level)
2. The uncertainty of each measurement can be reduced by taking average of a few readings. (e.g. Take many readings of t for each value of h and determine average <t>)</t>
3. Provide detials on how exact positions are located. (e.g. Centre of gravity of sphere obtained by finding diameter and hence radius using vernier callipers)
4. Use of large quantities to reduce percentage uncercainty. (e.g. Allow the ball bearing to fall through a long height to percentage uncertainity due to human reaction time is reduced.)
5. Allow time for equilibrium/stable state (e.g. Allow time for temperature to reach a steady state.)

Question 10

How to remove external influences

Answer 10

Perform the experiment in dark room to prevent external light sources.
Perform the experiment in sound proof room to minimise ambient noise.
Measure background radiation to determine actual count rate.

Question 11

How to conduct preliminary experiments

Answer 11

Conduct prelimnary experiments to choose a suitable range of values of IV that will give measurable values of DV.

Conduct prelimnary experiments to ensure that the change in values of IV that will lead to significant change in values of DV.

Question 12

Additional details

Answer 12

1. Description on the Use of complex apparatus
2. Method to ensure CV remains constant
3. Enchancing accuracy and reducing errors
4. Calibration of apparatus against a known quantiity
5. Removal of external influences
6. Conduct prelimnary experiments

Question 13

Safety precautions (Mechanics)

Answer 13

Mop up spllages of oil/water to avoid injuries due to fall

Cushion/sand in case load falls, keep feet away, keep distance from experiment
Wear safety boots so as to reduce possible injuries to the feet

Avoid the moving blades of the fan by using safety screen, switch off when chaging experiment

When handling glass, wear thick gloves to prevent injury

Question 14

Safety precautions (Thermal physics)

Answer 14

Wear heat insulating gloves
Do not touch the hot objects

Question 15

Safety precautions (Thermal physics)

Answer 15

Wear heat insulating gloves
Do not touch the hot objects

Question 16

Safety precautions (Waves)

Answer 16

Do not look directly at bright light source. Wear shades to protect the eyes.
Laser/light sources must not point directly at the experimenter.
Use heat insulating gloves when moving the hot light source.

Wear ear muffs, switch on sound source for short period of time

Question 17

Safety precautions (Electricity)

Answer 17

Wear rubber gloves to prevent burns as the wires may become hot.
Switch off power supply when not in use to avoid overheating of wire.
Do not touch coil because it is hot

(Do not mention electric shock when the current and voltage used are small)

Question 18

Safety precautions (Modern Physics)

Answer 18

The source is handled by a pair of tongs
The source is stored in a lead lined box when not in use
Avoid pointing source at people / do not look directly at source
Cordon off the area with tape and put up warning sign
Wear hazmat suit/protective clothing to protect from radiation.

Question 19

Compare 2 k values

Answer 19

Since the percentage difference in k (x%) is less than the percentage uncertainty of k (y%), k is considered to be a constant and my results support the suggested relationship.

Since the percentage difference in k (x%) is less than the percentage uncertainty of k (y%), k is considered not to be a constant and my result do not support the suggested relationship.

Question 20

Compare 4 k values

Answer 20

Since both k values in (a) are close to the values of k in (b), my result provide further evidence that the suggested relationship is valid.

Since both values of k in (a) are close to each other but significantly different from the k values in (b), my result provide evidence that the suggested relationship is only valid for a certain range of IV.

Since all values of k in (a) and (b) are significantly different from each other, this provides further evidence that the suggested relationship is not valid.

Question 21

Comment on anomaly

Answer 21

There are no anomalous points. The data points are scattered evenly about the best fit line.

There is one anomalous point because it is further from the best fit line compared to the other data points, while the rest of the data points are scattered evenly about the best fit line. The anomalous point is circled in the graph.