Experiments in L.C. Physics. By a Gentleman. MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR. Given the formula. MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR. Concave mirror. Crosswire. Lamp-box. Screen. u. v.
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Experiments in L.C. Physics By a Gentleman
MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR • Given the formula
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. (Mirror to sheet is approx. f measure with a meter stick) Place the lamp-box well outside the approximate focal length (Avoid a virtual image) Move the screen until a clear sharp 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 parralax when measuring with the meter rule and finding the exact position of the sharpest image.
VERIFICATION OF SNELL’S LAW OF REFRACTION Trace the ray of light to find i and r Glass Block
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 tableand Plot a graph of sin i against sin r. • The slope is refractive index, n • Do not use small i as then r too small to measure accurately
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. Use a metre stick. 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 (Use window focus method again/meter stick) • 2.Move the screen until a sharp 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 using the metre stick. • 5. Calculate the focal length of the lens using • 6. Repeat this procedure for different values of u. • Calculate f each time and then find the average value. • Avoid parralax
Cotton wool Boiling tube Water Copper rivets Heat source MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL OR WATER BY A MECHANICAL METHOD
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 • How do we measure it……. • Pretty much • Problems • Ice not all at same temperature • Covered in water • Heat loss/Gain to surroundings
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= mcalcc2+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.∆
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.(Alt measure string with metre stick and bob with verniercalipers and divide by 2 and add)
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 θon both sides and find average5. Calculate the distance d between the slits, using d=1/N the grating number. (e.g. N=300 lines/mm)Calculate the wavelength λusing nλ = dsinθ.6. Repeat this procedure for different values of n and get the average value for λ
Micrometer RESISTIVITY OF THE MATERIAL OF A WIRE Nichrome wire Crocodile clips l Metre stick Bench clamp Stand
Method 1. Note the resistance of the leads when the crocodile clips are connected together. Could also be precaution. 2.Stretch the wire enough to remove any kinks or ‘slack’ in the wire. 3.Read the resistance of the leads plus the resistance of wire between the crocodile clips from the ohmmeter. Subtract the resistance of the leads to get R. 4.Measure the length l of the wire between the crocodile clips, with the metre stick. 5.Increase the distance between the crocodile clips. Measure the new values of R and l and tabulate the results. 6.Make a note of the zero error on the micrometre. Find the average value of the diameter d.
1. Calculate the resistivity where A = 2. Calculate the average value for . Precautions Ensure wire is straight and has no kinks like .... Take the diameter of the wire at different angles
INVESTIGATION OF THE LAWS OF EQUILIBRIUM FOR A SET OF CO-PLANAR FORCES Support Newton balance Newton balance w2 w3 w1
1.Use balancing the metre stick on a fulcrum to find the centre of gravity and a digital scale to find the mass of the metre stick and its weight. 2.The apparatus was set up as shown and a equilibrium point found when system not moving. (Metre stick horizontal) 3.Record the reading on each Newton balance. 4. Record the positions 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.
MEASUREMENT OF THE SPEED OF SOUND IN AIR Tuning fork λ = 4(l1 + 0.3d) l1 d Graduated cylinder Tube Water
Method • Strike the highest frequency (512 Hz) tuning fork and hold it in a horizontal position just above the mouth of the tube. • Slide the tube slowly up from zero (To get fundamental frequency) until the note heard from the tube is at its loudest; resonance is now occurring. • Measure the length of the air column (from the water level to the top of the tube) l1 with a metre stick.
Method • An end correction factor has to be added to the length e = 0.3d, where d is the average internal diameter of the tube (measured using a vernier callipers). • Hence λ = 4(l1 + 0.3d) • c = f • c = 4f(l1 + 0.3d). • Calculate a value of c for each tuning fork and find an average value for the speed of sound.
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 one car and adjust so little drift when released) Set the weight F at 1 N (10 x 0.1N). 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.
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 vehicle placed on a level track should not drift toward either end) • 3.Measure the mass of each vehicle m1 and m2 respectively, including attachments, using a balance. • 4. Measure the length lof 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 = m1u momentum after the collision = (m1 + m2) v.Should be the same (Units are kg m/s)Repeat several times, with different velocities and different masses.
Questions Forces to be countered Friction – by cushion of air Gravity – level air track with a spirit level Measurements Mass, length of card and time to pass gate Calculations Velocity= Distance/time
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