Download electrical mechanical energy system la30-010

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
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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