If an electric motor is used to ift a known weight through a measured height we can calculate the useful energy output of the motor from the equation Work done = force x distance
We can also calculate the energy input from the motor using Electrical energy = VIt
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Photoelectric effect
A charged zinc plate is illuminated with a UV lamp through glass and the leaf remains charged (violet light only hitting it) but when the piece of glass is removed the leaf drops because UV light hits the zinc.
UV photons have energy greater than the work function and cause photoelectric emission.
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Measurement of resistance and production of I-V gr
A circuit with the component to be investigated and a variable power supply is needed.
An ammeter is connected in series with the component and a voltmeter in parallel.
Measurements of I and V can be taken as required and resistance calculated using the formula R = V/I.
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EMF and internal resistance of a cell
A circuit is set up with a cell, a resistor, an ammeter and a voltmeter in parallel with the cell.
The resistance of the circuit is changed to obtain a set of values of I the current through the cell and V the potential difference across the cell.
A graph is plotted of V on the y-axis and I on the x-axis and the y-intercept gives the EMF and the gradient gives the negative value of the internal resistance (V = -rI + E).
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Demonstation of drift velocity of ions
Use of copper sulphate and potassium pomanganate on a piece of soaked filter paper to measure how quickly the different coloured ions travel from plus to minus or vice versa.
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Resistivity of a metal wire
Set up a circuit with a 1m length of wire and an ammeter in series and a voltmeter in parallel.
Measure the resistance of the wire and repeat for lengths 90cm, 80cm etc down to 10cm.
Measure the diameter of the wire and calculate the cross sectional area.
Plot a graph of resistance on the y-axis against length on the x-axis.
Find the gradient and multiply it by the c.s.a to find the resistivity.
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Resistivity of polythene
Polythene is a very poor conductor of electricity so to lower the resistance a very large area and very small length is used (R = pl/A).
This enables us to measure the very small current produced and calculate the resistivity.
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Measurement of refractive index
Draw around a rectangular glass block
Use a protractor to mark in the normal
Measure the angle of incidence i and the angle of refraction r for a number of incident rays.
Plot a graph of sin i against sin r.
The gradient = the refractive index
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Rotation of the plane of polarisation using a suga
Set up two polarising filters whose planes of polarisation are at 90 degress.
Measure the angle using a protractor.
Insert the sugar solution in a boiling tube between the two filters and rotate until minimum light level is reached.
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