Experiments in L.C. Physics By a Gentleman
Dual timer Photogate l Pulley Light beam Card Slotted weights s Air track TO SHOW THAT aµ F t2 t1
Dual timer Photogate Light beam TO SHOW THAT aµ F t1 t1 time for card to pass first photo-gate
Dual timer Photogate Light beam TO SHOW THAT aµ F t1 t2 t2 time for card to pass second photo-gate
Procedure Set up the apparatus as in the diagram. Make sure the card cuts both light beams as it passes along the track. Level the air track. Set the weight F at 1 N. Release the vehicle. Note the times t1 and t2. Remove one 0.1 N disc from the slotted weight, store this on the vehicle, and repeat. Continue for values of F from 1.0 N to 0.1 N. Use a metre-stick to measure the length of the card l and the separation of the photo gate beams s.
a • 1/. Remember to include the following table to get full marks. All tables are worth 3 marks when the Data has to be changed. Draw a graph of a/m s-2 against F/N Straight line though origin proves Newton's second law
VERIFICATION OF THE PRINCIPLE OF CONSERVATION OF MOMENTUM l Card Vehicle 2 Dual timer t1 t2 Photogate Light beam Air track Vehicle 1 Velcro pad
Set up apparatus as in the diagram. • 2. Level the air-track.To see if the track is level carry out these tests: • a) A vehicle placed on a level track should not drift toward either end. • Measure the mass of each vehicle m1 and m2 respectively, including attachments, using a balance. • 4. Measure the length l of the black card in metres. • 5. With vehicle 2 stationary, give vehicle 1 a gentle push. After collision the two vehicles coalesce and move off together. • 6 Read the transit times t1and t2 for the card through the two beams.
Calculate the velocity before the collision, and after the collision, momentum before the collision=momentum after the collision, m1u = (m1 + m2) v.Repeat several times, with different velocities and different masses.
MEASUREMENT OF g Electromagnet Electronic timer Switch Ball bearing h Trapdoor
When the switch opens the ball falls The timer records the time from when the switch opens until trap door opens
When the switch opens the ball falls The timer records the time from when the switch opens until trap door opens
Set up the apparatus. The millisecond timer starts when the ball is released and stops when the ball hits the trapdoor Measure the height h as shown, using a metre stick. Release the ball and record the time t from the millisecond timer. Repeat three times for this height h and take the smallest time as the correct value for t. Repeat for different values of h. Calculate the values for g using the equation . Obtain an average value for g. Place a piece of paper between the ball bearing and the electromagnet to ensure a quick release
Volume scale Tube with volume of air trapped by oil Bicycle pump Reservoir of oil Valve Pressure gauge VERIFICATION OF BOYLE’S LAW
Using the pump, increase the pressure on the air in the tube. Close the valve and wait 20 s to allow the temperature of the enclosed air to reach equilibrium. • Read the volume V of the air column from the scale. • Take the corresponding pressure readingfrom the gauge and record the pressure P of the trapped air. • Reduce the pressure by opening the valve slightly – this causes an increase the volume of the trapped air column. Again let the temperature of the enclosed air reach equilibrium. • Record the corresponding values for the volume V and pressure P . • Repeat steps two to five to get at least six pairs of readings.
P 1/V Plot a graph of P against 1/V. A straight-line graph through the origin will verify that, for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume, i.e. Boyle’s law.
INVESTIGATION OF THE LAWS OF EQUILIBRIUM FOR A SET OF CO-PLANAR FORCES Support Newton balance Newton balance w2 w3 w1
1.Use a balance to find the centre of gravity of the metre stick and its weight. 2.The apparatus was set up as shown and a equilibrium point found. 3.Record the reading on each Newton balance. 4. Record the postions on the metre stick of each weight, each Newton balance and the centre of gravity of the metre stick
For each situation (1) Forces up = Forces downi.e. the sum of the readings on the balances should be equal to the sum of the weights plus the weight of the metre stick. (2)The sum of the clockwise moments about an axis through any of the chosen points should be equal to the sum of the anticlockwise moments about the same axis.
INVESTIGATION OF THE RELATIONSHIP BETWEEN PERIOD AND LENGTH FOR A SIMPLE PENDULUM AND HENCE CALCULATION OF g l Split cork Timer Bob 20:30
1.Place the thread of the pendulum between two halves of a cork and clamp to a stand.2.Set the length of the thread at one metre from the bottom of the cork to the centre of the bob. 3.Set the pendulum swinging through a small angle (<10°). Measure the time t for thirty complete oscillations.4.Divide this time t by thirty to get the periodic time T.5.Repeat for different lengths of the pendulum.
MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR Concave mirror Crosswire Lamp-box Screen u v
Approximate focal length by focusing image of window onto sheet of paper. Place the lamp-box well outside the approximate focal length Move the screen until a clear inverted image of the crosswire is obtained. Measure the distance u from the crosswire to the mirror, using the metre stick. Measure the distance v from the screen to the mirror. Repeat this procedure for different values of u. Calculate f each time and then find an average value. Precautions The largest errors are in measuring with the meter rule and finding the exact position of the sharpest image.
VERIFICATION OF SNELL’S LAW OF REFRACTION Lamp-box 0 - 360° Protractor i Glass Block r
Place a glass block on the 0-3600 protractor in the position shown on the diagram and mark its outline. • Shine a ray of light from a lamp-box at a specified angle to the near side of the block and note the angle of incidence. • Mark the exact point B where it leaves the glass block. • Remove the glass block. Join marks to trace ray.
sin i sin r. • Measure the angle of refraction r with protractor. • Repeat for different values of i. • Draw up a table and Plot a graph of sin i against sin r. • The slope is refractive index, n
Cork Pin Apparent depth Mirror Real depth Water Image Pin MEASUREMENT OF THE REFRACTIVE INDEX OF A LIQUID
Finding No Parallax – Looking Down Pin at bottom Pin reflection in mirror No Parallax Parallax
Set up the apparatus as shown. Adjust the height of the pin in the cork above the mirror until there is no parallax between its image in the mirror and the image of the pin in the water. Measure the distance from the pin in the cork to the back of the mirror – this is the apparent depth. Measure the depth of the container – this is the real depth. Calculate the refractive index n= Real/Apparent Repeat using different size containers and get an average value for n.
Lamp-box with crosswire Screen Lens v u MEASUREMENT OF THE FOCAL LENGTH OF A CONVERGING LENS
1.Place the lamp-box well outside the approximate focal length 2.Move the screen until a clear inverted image of the crosswire is obtained. 3.Measure the distance u from the crosswire to the lens, using the metre stick. 4. Measure the distance v from the screen to the lens. 5. Calculate the focal length of the lens using 6. Repeat this procedure for different values of u. 7. Calculate f each time and then find the average value.
Metre stick Laser x θ D Diffraction grating MEASUREMENT OF THE WAVELENGTH OF MONOCHROMATIC LIGHT n = 2 n = 1 n = 0 n = 1 Tan θ = x/D n = 2
1. Set up the apparatus as shown.Observe the interference pattern on the metre stick – a series of bright spots.2.Calculate the mean distance x between the centre (n=1) bright spot and the first (n =1) bright spot on both sides of centre.3.Measure the distance D from the grating to the metre stick.4.Calculate θ.5.Calculate the distance d between the slits, using d=1/N the grating number.Calculate the wavelength λusing nλ = dsinθ. 6. Repeat this procedurefor different values of n and get the average value for λ
CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A STANDARD Multimeter as ohmmeter Mercury thermometer Boiling tube Water Glycerol Thermistor Heat source
1. Set up apparatus as shown in the diagram. 2. Place the mercury thermometer and the thermistor in the boiling tube. 3. Record the temperature ,in C, from the mercury thermometerand the corresponding thermistor resistance R, in ohms, from the ohmmeter. 4. Increase the temperature of the glycerol by 5C. 5. Again record the temperature and the corresponding thermistor resistance. 6. Repeat the procedure until at least ten sets of readings have been recorded. 7. Plot a graph of resistance R against temperature and join the points in a smooth, continuous curve.
MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL BY AN ELECTRICAL METHOD Metal block 12 V a.c. Power supply Joulemeter 10°C 350 J Heating coil Glycerol Lagging
1.Find the mass of the metal block m. 2.Set up the apparatus as shown in the diagram. 3.Record the initial temperature θ1 of the metal block. 4.Plug in the joulemeter and switch it on. 5.Zero the joulemeter and allow current to flow until there is a temperature rise of 10 C. 6. Switch off the power supply, allow time for the heat energy to spread throughout the metal block and record the highest temperature θ2. 7. The rise in temperature is therefore θ2 – θ1. 8. Record the final joulemeter reading Q. Energy supplied electrically = Energy gained by metal block Q = mc.
MEASUREMENT OF SPECIFIC HEAT CAPACITY OF WATER BY AN ELECTRICAL METHOD Joulemeter 12 V a.c. Power supply Cover Digital thermometer Water Lagging Calorimeter Heating coil 10°C 350 J
1.Find the mass of the calorimeter mcal. 2.Find the mass of the calorimeter plus the water m1. Hence the mass of the water mw is m1 – mcal. 3.Set up the apparatus as shown. Record the initial temperature θ1. 4.Plug in the joulemeter , switch it on and zero it. 5.Switch on the power supply and allow current to flow until a temperature rise of 10 C has been achieved. 6. Switch off the power supply, stir the water well and record the highest temperature θ2. Hence the rise in temperature is θ2 – θ1. 7. Record the final joulemeter reading Q.
Electrical energy supplied = energy gained by (water +calorimeter) Q = mwcw + mcalccal. Precautions 1/. Lagging 2/. Cool water slightly so final temperature not far from room temperature.
Cotton wool 10°C Boiling tube Water Digital thermometer Copper rivets Water Lagging Calorimeter Heat source MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL OR WATER BY A MECHANICAL METHOD
1.Place some copper rivets in a boiling tube. Fill a beaker with water and place the boiling tube in it. 2.Heat the beaker until the water boils. Allow boiling for a further five minutes to ensure that the copper pieces are 100° C. 3.Find the mass of the copper calorimeter mcal. 4.Fill the calorimeter, one quarter full with cold water. Find the combined mass of the calorimeter and water m1. 5.Record the initial temperature of the calorimeter plus water θ1.Place in lagging 6.Quickly add the hot copper rivets to the calorimeter, without splashing. 7.Stir the water and record the highest temperature θ2. 8.Find the mass of the calorimeter plus water plus copper rivets m2 and hence find the mass of the rivets mco.
6.Quickly add the hot copper rivets to the calorimeter, without splashing. 7.Stir the water and record the highest temperature θ2. 8.Find the mass of the calorimeter plus water plus copper rivets m2 and hence find the mass of the rivets mco. Heat lost by the Riverts=Heat gained by water and calorimeter mco cco = mw cw +mc cc
MEASUREMENT OF THE SPECIFIC LATENT HEAT OF FUSION OF ICE 10°C Wrap ice in cloth to crush and dry. Crushed ice Digital thermometer Calorimeter Water Lagging
1.Place some ice cubes in a beaker of water and keep until the ice-water mixture reaches 0 °C. 2.Find the mass of the calorimeter mcal. Surround with lagging 3.Half fill the calorimeter with water warmed to approximately 10 °C above room temperature. Find the combined massof the calorimeter and water m2. 4.Record the initial temperatureθ1 of the calorimeter plus water. 5.Surround the ice cubes with kitchen paper or a cloth and crush them between wooden blocks – dry them with the kitchen paper. 6.Add the pieces of dry crushed ice, a little at a time, to the calorimeter. 7.Record the lowest temperature θ2 of the calorimeter. Find the mass of the calorimeter + water + melted ice m3
CalculationsEnergy gained by ice = energy lost by calorimeter + energy lost by the water.mil +micw1= mcalcc 2+mwcw 2
MEASUREMENT OF THE SPECIFIC LATENT HEAT OF VAPORISATION OF WATER Lagging Water Heat source 10°C Digital Thermometer Steam Trap Calorimeter
1.Set up as shown 2.Find the mass of the calorimeter mcal. 3.Half fill the calorimeter with water cooled to approximately 10 °C below room temperature. 4.Find the mass m1 of the water plus calorimeter. 5.Record the temperature of the calorimeter + water θ1. 6.Allow dry steam to pass into the water in the calorimeter until temperature has risen by about 20 °C. 7.Remove the steam delivery tube from the water, taking care not to remove any water from the calorimeter in the process. 8.Record the final temperature θ2 of the calorimeter plus water plus condensed steam. 9.Find the mass of the calorimeter plus water plus condensed steam m2.
Energy lost by steam = energy gained by calorimeter + energy gained by the watermsl+mscw∆ = mcalcc ∆+mwcw.∆