The Student Room Group

Damping and Oscillations

Screenshot from 2019-02-28 10-33-40.png

The magnet on the spring is displaced downwards and released and a graph of amplitude against time is plotted. Now the resistance of the resistor R is increased and the same procedure is repeated. How will the graph now look like?

The markscheme says that the damping would be lesser. But since the resistance R is increased, there is more energy lost and hence the damping would be greater right? Can anyone please explain me this. Thank you for help :smile:.
Original post by esrever
Screenshot from 2019-02-28 10-33-40.png

The magnet on the spring is displaced downwards and released and a graph of amplitude against time is plotted. Now the resistance of the resistor R is increased and the same procedure is repeated. How will the graph now look like?

The markscheme says that the damping would be lesser. But since the resistance R is increased, there is more energy lost and hence the damping would be greater right? Can anyone please explain me this. Thank you for help :smile:.


resistance going up doesn't mean increased power dissipation
P=ℰ/R2

the consequence is that if you made the coil out of insulating material it might as well not be there at all
or if you made it out of a superconductor (with no added resistor) the Lenz's law reaction force would levitate the magnet
Reply 2
Original post by Joinedup
resistance going up doesn't mean increased power dissipation
P=ℰ/R2

the consequence is that if you made the coil out of insulating material it might as well not be there at all
or if you made it out of a superconductor (with no added resistor) the Lenz's law reaction force would levitate the magnet

What is the symbol?
Original post by esrever
What is the symbol?

e.m.f. but in this case is induced emf.
Reply 4
Original post by Joinedup
resistance going up doesn't mean increased power dissipation
P=ℰ/R2

the consequence is that if you made the coil out of insulating material it might as well not be there at all
or if you made it out of a superconductor (with no added resistor) the Lenz's law reaction force would levitate the magnet

But P = I^2 R as well right?
Original post by esrever
But P = I^2 R as well right?

Resistance being the tendency to reduce the flow of electric current, right?

Current (if any) is the consequence of the EMF induced by moving the magnet into the coil - R goes up and I goes down... and I2 going down faster than R is going up.
Reply 6
Original post by Joinedup
Resistance being the tendency to reduce the flow of electric current, right?

Current (if any) is the consequence of the EMF induced by moving the magnet into the coil - R goes up and I goes down... and I2 going down faster than R is going up.

So emf is constant while the current depends on the resistance right?
Original post by esrever
So emf is constant while the current depends on the resistance right?

Be careful when you say emf is constant. In fact, the induced emf is sinusoidal for this oscillating magnet case.

Current should depend on resistance when emf varies the same way.

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