practicals

Question 1

Measurement of the density of solids

Answer 1

calculate the density using: ρ = m/V use a displacement can to measure volume

Question 2

Measurement of g by freefall

Answer 2

s = ut + 1/2mv^2 and either 1. Manual timing - This method has a lot of inherent errors, and gives poor results. from slow reaction time and parallax .or
2. Using lightgates - Lightgates are very accurate, and a viable alternative for high precision results

Question 3

Investigation of Newton’s 2nd law

Answer 3

mg = (M + m)
Fix the thread to the rider and attach masses to the other end. Set the light gates to record the acceleration and allow the masses to fall to the ground.
Repeat the experiment until all the different accelerating masses have been removed. Plot a graph of acceleration (y-axis) against gravitational force, mg (x-axis). This should be a straight line through the origin.

Question 4

Determination of Young modulus of a metal in the form of a wire

Answer 4

Young modulus = Stress/strain

Question 5

Investigation of the force-extension relationship for rubber

Answer 5

Apparatus:
• Rubber band of cross-section approximately 1 mm by 2 mm
9 We use this method to eliminate any thermal extension/contraction
10 Measuring at several places along the length is a favourite of exam boards.
Figure 5: Young’s Modulus apparatus
• Clamp and stand G-clamp to secure (if required) 50 g mass holder plus a number of 50 g masses
• Optical pin (for use as a pointer if required)
• Metre rule (resolution ±0.001m) Micrometer (resolution ±0.01mm)
Experimental Method:
Hang a (cut) rubber band of (approximate) cross-section 1 mm by 2 mm vertically from a stand, boss and clamp. The base of the stand should be secured using a G-clamp. Hang a 50 gram mass holder from the band. Place a metre rule close to the mass holder. The length can be read using an optical pin attached to the base of the mass holder. Measure the length, width and thickness of the rubber when it is supporting the 50 gram holder. Increase the mass in steps, measuring the extension each time. Continue until the band breaks.11 Plot the force - extension curve and determine the Young modulus from the linear section.

Question 6

I-V characteristics of the filament of a lamp and a metal wire at con- stant temperature

Answer 6

Apparatus:
• Variable d.c. voltage supply
• Switch
• Ammeter
• Voltmeter
• Component
Starting with the output of the variable d.c. voltage supply set to its minimum value increase the value of the  voltage. The current through the component and the potential difference across the component is recorded for a range of values of the applied voltage. A graph of current against voltage is plotted.

Question 7

Measurement of the intensity variations for polarisation

Answer 7

Apparatus:
• Two pieces of polaroid
• Lamp
Investigate the variation in intensity by looking through the lamp through both polaroids and rotating one of the polaroids through 360°.
Note the change in intensity that occurs.

Question 8

Determination of wavelength using Young’s double slits

Answer 8

Apparatus:
• Laser pen
• Stand and clamp
• Double slit
• Screen
• Metre rule
• 30 cm ruler or digital callipers

Question 9

Determination of wavelength using a diffraction grating

Answer 9

Apparatus:
• Laser
• Diffraction grating of known d value or ruling e.g. 300 lines cm−1 • Metre rule
• Screen
• Stand and clamp for laser and grating
nλ = d sin θ

Question 10

Determination of the speed of sound using stationary waves

Answer 10

When resonance first occurs the length of air in the tube, l, plus a small end correction, e (to account for the position of the tuning fork
above the tube) will be equal to a quarter of a wavelength. Hence: l + e = λ/4

Experimental method:

Initially place the resonance tube as deep as possible into the water. Then gradually raise it. As this is being done hold a vibrating tuning fork over the top. When resonance occurs (a loud sound will be heard) measure the length of the tube above the water level. Repeat the above for each of the tuning forks. Plot a graph of length (y-axis) against 1/frequency (x-axis). Use the gradient to determine a value for the speed of sound.

Question 11

Investigation of the variation of resistance with temperature for a metal wire

Answer 11

Apparatus:
• Bunsen burner; tripod, gauze and stand • 250 ml beaker of water
• Ice 18
• Thermometer0°Cto100°C
• Multimeter set on ohm range to measure resistance • Copper coil
• Stirrer

The water bath should be heated and the water stirred continuously in order to ensure an even temperature throughout the water bath. Once the required tempera- ture has been reached then remove the heat and record the reading of resistance or take the ammeter and voltmeter readings. This pro- cess should be repeated at intervals until the water boils. Repeat the experiment during cooling. Plot a graph of resistance (y-axis) against temperature (x-axis).

Question 12

Investigation of the variation of resistance with temperature for a metal wire

Answer 12

Apparatus:
• Bunsen burner; tripod, gauze and stand • 250 ml beaker of water
• Ice 18
• Thermometer0°Cto100°C
• Multimeter set on ohm range to measure resistance • Copper coil
• Stirrer

The water bath should be heated and the water stirred continuously in order to ensure an even temperature throughout the water bath. Once the required tempera- ture has been reached then remove the heat and record the reading of resistance or take the ammeter and voltmeter readings. This pro- cess should be repeated at intervals until the water boils. Repeat the experiment during cooling. Plot a graph of resistance (y-axis) against temperature (x-axis).