help! (1 Viewer)

[sanjeevprasad99]

Q) A hand generator is connected to a light box in series with a switch. Is it easier to turn the coil when the switch is open or when it is closed? Explain your reasoning


i got that it wouldn’t matter coz there would still b a change in magnetic flux occurring and therefore induced emf, and a therefore a force opposing motion......am i wrong?

 

[helper]

A force will only exist when there is a current flowing. When the switch is open no current flows, so no force will exist F=BIl=F=Blx0=0

When the switch is closed a current starts to flow and a force exists that makes it harder to turn.

 

[sanjeevprasad99]

oo, i get ya, thanks!

 

[Forbidden.]

Is there any mention of Lenz's Law here ?

 

[sanjeevprasad99]

Is there any mention of Lenz's Law here ?

nope, it just says that.....

 

[sanjeevprasad99]

.......what about faradays law and induced emf?....can someone explain y there would b no induced emf? and therefore no force(in relation to faradays law)?
not: A force will only exist when there is a current flowing. When the switch is open no current flows, so no force will exist F=BIl=F=Blx0=0

When the switch is closed a current starts to flow and a force exists that makes it harder to turn.

 

[helper]

Faraday's law does produce a induced EMF in this case. So for an instant in time there will be a current as this occurs.

However after that instant the current will not continue as the resistance of the circuit is too high, so no current will then flow. An EMF without a current does not produce a force.

 

[sanjeevprasad99]

Faraday's law does produce a induced EMF in this case. So for an instant in time there will be a current as this occurs.

However after that instant the current will not continue as the resistance of the circuit is too high, so no current will then flow. An EMF without a current does not produce a force.

yeah, i see what u mean, but how is the resistance of the circuit too high? and if there is a emf, then isnt there current as well?

 

[Forbidden.]

yeah, i see what u mean, but how is the resistance of the circuit too high? and if there is a emf, then isnt there current as well?

Or you could say induced current.

 

[helper]

The resistance of the circuit includes the resistance of the switch. When the switch is closed the switches resistance is zero, so there is only the resistance of the circuit. This allows the current to flow.

When the switch is open, its resistance is very high, so the resistance of the circuit is very high. For a current to flow around the circuit the EMF would have to be high enough to allow charges to jump the sir gap in the switch.

Originally the positive and negative particles are arranged randomly.
The induced EMF results in one side becoming positive and the other negative.
Once this charge separation becomes large enough it will stop any more electrons moving and the current stops.

If there is an external circuit joining the positive and negative sections of the generator then the electrons can then move around the circuit and balance back up. That is what happens when the light is on.

If there is no external circuit then the current stops as soon as the force due to the separation of charges equals the force you are applying to the charges in the generator.

 

[Forbidden.]

The resistance of the circuit includes the resistance of the switch. When the switch is closed the switches resistance is zero, so there is only the resistance of the circuit. This allows the current to flow.

When the switch is open, its resistance is very high, so the resistance of the circuit is very high. For a current to flow around the circuit the EMF would have to be high enough to allow charges to jump the sir gap in the switch.

Originally the positive and negative particles are arranged randomly.
The induced EMF results in one side becoming positive and the other negative.
Once this charge separation becomes large enough it will stop any more electrons moving and the current stops.

If there is an external circuit joining the positive and negative sections of the generator then the electrons can then move around the circuit and balance back up. That is what happens when the light is on.

If there is no external circuit then the current stops as soon as the force due to the separation of charges equals the force you are applying to the charges in the generator.

Band theory plays a role in any of those explanations ?

 

[helper]

They could but not really needed. All it comes down to is a switch that is on has zero resistance. When the switch is off it has such a high resistance it stops current flowing.

 

[sanjeevprasad99]

The resistance of the circuit includes the resistance of the switch. When the switch is closed the switches resistance is zero, so there is only the resistance of the circuit. This allows the current to flow.

When the switch is open, its resistance is very high, so the resistance of the circuit is very high. For a current to flow around the circuit the EMF would have to be high enough to allow charges to jump the sir gap in the switch.

Originally the positive and negative particles are arranged randomly.
The induced EMF results in one side becoming positive and the other negative.
Once this charge separation becomes large enough it will stop any more electrons moving and the current stops.

If there is an external circuit joining the positive and negative sections of the generator then the electrons can then move around the circuit and balance back up. That is what happens when the light is on.

If there is no external circuit then the current stops as soon as the force due to the separation of charges equals the force you are applying to the charges in the generator.

thanks dude, u know ur phys better than my teacher!!!!

 

[xiao1985]

well answered.

though from my understanding, opened switch implies no current flowing. (though it reaches the same conclusion)