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dynamo effect on my bike
Why does a dynamo slow down my bike, and why does this retardation effect increase, the greater the load on the dynamo??
A dynamo is a little electrical generator, basically. When you pedal your bike, a small voltage is induced by the dynamo which can be used to power useful things like lights.
The induced voltage produced by the dynamo, when connected to a load like a lamp, draws a current through that lamp. Unfortunately this current, when moving within a magnetic field, (in this case present because of the dynamo), produces a force which opposes the motion that created that current in the first place. ie. the forward rotary motion of your wheels. This explains why the dynamo will work to slow your bike down.
As you increase the load on the dynamo, for instance by using a larger lamp that requires more current, you will need to pedal faster to generate a larger induced voltage within the dynamo to power the lamp. By doing this, a larger current is drawn and a larger force is therefore produced that, as always, will oppose the motion of the wheels. This larger force will therefore produce a greater decelleration on your bike.
If you have any more questions, feel free to ask
The induced voltage produced by the dynamo, when connected to a load like a lamp, draws a current through that lamp. Unfortunately this current, when moving within a magnetic field, (in this case present because of the dynamo), produces a force which opposes the motion that created that current in the first place. ie. the forward rotary motion of your wheels. This explains why the dynamo will work to slow your bike down.
As you increase the load on the dynamo, for instance by using a larger lamp that requires more current, you will need to pedal faster to generate a larger induced voltage within the dynamo to power the lamp. By doing this, a larger current is drawn and a larger force is therefore produced that, as always, will oppose the motion of the wheels. This larger force will therefore produce a greater decelleration on your bike.
If you have any more questions, feel free to ask
Reply 2
One last thing. Why does the retarding effect diminish, as speed falls?
Reply 4
As the speed falls, the revolutuin per second of dynamo reduces which decrease rate of change magnetic field. According to the law of electromagnetic induction, the change in rate of change of magnetic flux will try to oppose the change and inturn produces an effective force to counter it. Therefore, the retarding effect reduces.
Reply 5
it is not a smaller opposing force to the motion, the force induced in the curcuit tries to accelarate the bime therefore retardation decreases
driving_seat
it is not a smaller opposing force to the motion, the force induced in the curcuit tries to accelarate the bime therefore retardation decreases
This is incorrect.
The dynamo does not try to accelerate the bike, otherwise the cyclist would get energy for nothing, which cannot happen, ever. Lenz's Law, which is basically tan energy conservation law, states that the a conductor moving within a magnetic field will induce a voltage that will then draw a current if there's a load present. That current will always produce a force opposing the motion that created it. In the case of the bicycle dynamo, the forward motion of the wheels induces voltage and subsequent current, so the force created by that current acts to oppose the forward motion of the bike.
The induced voltage is directly proportional to the rate of revolution of the bicycle wheels and inducing a larger voltage will draw a larger current through the load. A larger current will produce a larger force for a given magnetic field, since in a current carrying conductor F=BIL. So speeding up works to decellerate the bike more, and slowing down will decellerate the bike less.
Reply 7
Eddie K
The dynamo does not try to accelerate the bike, otherwise the cyclist would get energy for nothing, which cannot happen, ever. Lenz's Law, which is basically tan energy conservation law, states that the a conductor moving within a magnetic field will induce a voltage that will then draw a current if there's a load present. That current will always produce a force opposing the motion that created it. In the case of the bicycle dynamo, the forward motion of the wheels induces voltage and subsequent current, so the force created by that current acts to oppose the forward motion of the bike.
The dynamo does not try to accelerate the bike, otherwise the cyclist would get energy for nothing, which cannot happen, ever. Lenz's Law, which is basically tan energy conservation law, states that the a conductor moving within a magnetic field will induce a voltage that will then draw a current if there's a load present. That current will always produce a force opposing the motion that created it. In the case of the bicycle dynamo, the forward motion of the wheels induces voltage and subsequent current, so the force created by that current acts to oppose the forward motion of the bike.
Yeah! I meant thew same :P
Reply 8
You get a Form of Back EMF when the dynamo is spinning up, a bit like when you start a drill and it takes a few seconds to accelerate to speed because the back EMF created by the motor is equalling the rotation and eventually the values become closer and it stops accelerating.
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