Apparatus* Ammeter* Bar magnet* Coil* Connecting wires* Metre Rule* Power supply (0-12V d.c.
supply)* String – 2 pieces of equal length 20 cm* Set of masses ranging from 1g to 50g* Spirit level* Blocks of wood* Variable resistorIn my experiment I shall set up the apparatus as above. I have chosen to use a piece of wire which is 2m long and shall be wrapped round a cardboard tube so that it has 200 complete turns which will directly next to each other. I have chosen to leave no gaps as then the spacing between them will be equal which will mean the intensity of magnetism will be the same throughout the coil.To calculate the force exerted between the magnet and coil I shall be using the principle of moments. My metre stick shall be pivoted exactly in the centre (at 50cm mark) to make my measurements more accurate. I shall then attach the magnet to the left hand end of the metre stick with string; the string will be of length 20cm and marked at every 1cm interval as will the magnet.On the right hand end of the metre rule I shall place a piece of string also of 20 cm along to the end of the piece of the string I shall attach masses until the metre becomes balanced and is in equilibrium.
I would use the spirit level for extra accuracy to guarantee it was perfectly balanced. I would then calculate the force acting on the magnet when there was not a current running through the coil. To calculate the force I would use the equation for the principle of moments.FORCE= MASS x PEPENDICULAR DISTANCE FROM ACTING FORCEe.g.Say that a mass of 20g was placed on the right hand side and the distance x was 50cm then:-FORCE= MASS x PEPENDICULAR DISTANCE FROM ACTING FORCE= (20/1000) x (50/1000)= 0.001 NTherefore due to equal and opposite forces the force downwards being caused by the magnet is the same as the force being caused downwards by the mass as they are in equilibrium.
I decided that the current would run from the bottom of the coil upwards, I decided this by using Flemings right hand grip rule.To monitor the magnitude of the current I shall be using a variable resistor in my circuit to make sure I have a constant current of 5 amperes (or 5A) and to measure the magnitude of current I shall use a digital ammeter which has a low resistance so it does not alter the current to much in the circuit.To measure the distance x I shall lower the clamp stand and using the markings on the string and magnet at every 1cm lower the clamp stand until it is at the height that I require. I would then switch the power pack on at 6V and make sure the current was at 5A and if it was not to adjust it using the variable resistor. The coil would then attract the magnet and pull it downwards to calculate the force I would place further mass slots on the right hand side until it was balanced again, to check it was in equilibrium I would use a spirit level. To calculate the force I would use the formulaFORCE= MASS x PEPENDICULAR DISTANCE FROM ACTING FORCEe.g.
Say at a distance of x= 3cm, I added a further 15 g (to the 20g that was needed to balance the magnet) to the right hand side to balance the metre rule while the magnet was in the coil and both had a perpendicular distance of 50 cm.FORCE= MASS x PEPENDICULAR DISTANCE FROM ACTING FORCE=(0.020+0.015) x 50= 1.75NThere for the magnitude of the attractive force between the magnet and the coil would be 1.75 NI would then repeat my readings twice for every value of x to reduce random error.I would then plot my results in a table similar to the one below:-Distance x/mMass added to right hand side/g1Mass added to right hand side/g2Mass added to right hand side/gAverageForce/NForce= mass x perpendicular distance from acting force0.
0070.0080.0090.010I would then plot Force on the y-axis and distance on the x-axis like this:-Features in my experiment which makes it more accurate are;* Spirit level as it is insured that the experiment is balanced and I therefore get the correct values for force.* Try and get the whole in the middle of the metre stick toe reduce error when calculating the moments* A variable resistor so I can change the current if it changes at any point in the experiment.