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ELECTRICAL MECHANICAL ENERGY SYSTEM LA30-010 INSTRUCTIONS FOR USE ELECTRICAL-MECHANICAL ENERGY SYSTEM LA 30-010 INTRODUCTION One of the most productive areas for investigation at either KS3/4 or A-Level is the interchange between electrical and mechanical energy. It allows all the areas of power, work done, potential energy, electrical energy and efficiency to be explored with the corresponding practise of these calculations and concepts. This apparatus provides a reliable and foolproof method of tackling this area of work. A small electric motor rotates a shaft which winds up a thread attached to a load. The gearing and cut-out system ensure that sensible measurements can be taken without damage to any of the essential components. APPLICATIONS Mechanical energy calculations Electrical energy calculations Efficiency calculations Electrical and mechanical measurement skills OPERATION Place the apparatus on the bench with the base cut-out overhanging the edge. Connect the two input sockets to a variable low voltage power supply in series with a moving coil ammeter reading to 1A FSD. Monitor the voltage applied to the sockets with a moving coil voltmeter capable of reading to 5V FSD. Note that some digital meters might prove satisfactory but many give erratic results when monitoring small electric motors due to their sampling rate. Attach one loop of the thread to the hub screw in the large gear wheel near the motor. Pass the thread over the pulley, through the slot in the sensor arm and down to a slotted mass carrier. This can be either 0 - 100g or 0 - 1000g but note that the maximum load is 600g. Ensure that the top of the mass carrier is free to pass through the base cut-out to lift the sensor arm when it reaches the top of its travel. Put the control switch to the mid (OFF) position and switch on the power supply adjusting the output to about 1.5V initially. Ensure that the sensor arm is down and then move the switch to UP. The load should be lifted at a steady rate as the thread winds up on the shaft and as the top of the carrier lifts the sensor arm, the motor will stop. Move the switch to the OFF position. To return the load to the bottom of its travel, manually move the gear wheel one or two turns to lower the load a few centimetres. Move the switch to DOWN. The motor will reverse and return the load to the bottom. Move the switch to OFF when it is fully unwound. The system is now ready for use again. NOTE: The maximum input voltage is 3V, maximum current is 1A and the maximum load is 6N. Under stall conditions the motor current can rise to much higher values and can burn out the windings. Steps should be taken to ensure that students cannot operate the system above the maximum ratings and it is generally better to limit work below these ratings to leave a safety margin. PTO Measurements Input power is calculated from P = IV where the current I is in amps and the voltage V is in volts. Power is then in watts. Measure the time taken (t in seconds) for the load (m in kg) to be lifted a certain height (h in metres). The output power can be calculated from P = mgh/t. Efficiency is calculated from Output power / Input power and is expressed as a percentage by multiplying by 100. Investigations How is the rise time for a given load related to the input power. How is the rise time for a given load related to the input voltage. How is the rise time related to load for a given input voltage. How does the efficiency of the system vary with different loads. How does the efficiency vary with input power for a given load. There are many other variations on these and in all cases the other variables have to be noted and controlled offering great scope for very detailed and flexible experimental work. Lascells Ltd., Walkmill Business Park, Sutton Road, Market Drayton, Shropshire TF9 2HT Tel: 01630 657801