practicals

Question 1

Young’s double slit experiment -shows how light waves produce an interference pattern

Answer 1

Fringe width = wavelength x distance(m) / slit separation (m)

1. monochromatic light placed behind a single slit, light diffracted producing two light sources at double slits A & B
2. Both light sources from the same source = coherent - observable interference pattern.
3. Both diffracted light from double slits create interference pattern of bright &dark fringes
4. wavelength of light calculated from interference pattern & experiment set up.
5. Constructive interference = light
   Destructive interference = dark

Question 2

Acceleration of Free fall (g)

Answer 2

1. Current to magnet switches off, ball drops & timer starts
2. When ball hits trapdoor, timer stops
3. The time takes to fall a distance, h
4. repeated for different values of h

Question 3

Young’s módulos of a copper wire

Answer 3

1. Measure diameter of wire with micrometre at least 3 readings & average
2. Set up the apparatus so the wire is taut.
3. Measure OG length of wire using metre ruler & mark reference point with tape
4. Add 100 g mass onto mass hanger - record new reading of tape
5. Repeat adding a 100 g mass (at least 5 – 10 times)

Question 4

Equation for Young’s modulus

Answer 4

Tensile Stress / tensile strain

Question 5

Resistivity of a metal

Answer 5

1. Measure diameter using a micrometer Multiple measurements & average.
2. Set up equipment so wire clamped to ruler with one end of circuit attached to wire where the ruler reads 0.
3. The ammeter is connected in series and the voltmeter in parallel to the wire
4. Attach the flying lead to the test wire at 0.25 m & set voltage of 6.0 V.

5.Record current from ammeter, then switch off current immediately after reading (the short wire = hot)

6. Vary distance between fixed end of the wire and flying lead in 0.25 m intervals.
7. Record current for each length at least 3 times & calculate an average current

Question 6

Resistivity equation

Answer 6

R = pL /A

Resistance = Resistivity x length of wire (m)/ cross sec area of wire (m2)

Resistivity can also be calculated from gradient of resistance vs length graph multiplied by cross sectional area

Question 7

EMF & internal resistance

Answer 7

1. The cell & resistor connected in series
2. With switch open, record reading V on voltmeter
3. Set variable resistor to its maximum value, close the switch & record V and the reading I on ammeter - make sure to open the switch between readings
4. Vary resistance of variable resistor & record values for V and I for each resistance.