Do nowDo now::

Eventually, the current Eventually, the current will build up to it’s will build up to it’s maximum value:maximum value:

A

LR

V

RVI max

In your own words, describe what happens In your own words, describe what happens in this circuit when the switch is closedin this circuit when the switch is closed

Wednesday, May 3, 2023

Describe Faraday / Lenz’s law in detail!Describe Faraday / Lenz’s law in detail!

Changing CurrentChanging Current

I

t

Imax

I

t

Imax

Without Inductor With Inductor

Time ConstantTime Constant

The time constant The time constant is is defined as the time defined as the time taken for the current taken for the current to reach 63% of it’s to reach 63% of it’s maximum value.maximum value.

A circuit is said to be A circuit is said to be at maximum current at maximum current after 3 time constantsafter 3 time constants(same as caps)(same as caps)

63%

I

t

Imax

What do you think the time constant What do you think the time constant depends on?depends on?

The size of the inductorThe size of the inductor(bigger L means more back (bigger L means more back e.m.f / magentic field to fill, so e.m.f / magentic field to fill, so longer for current to reach max)longer for current to reach max)

The resistance of the circuit The resistance of the circuit (larger R means smaller circuit (larger R means smaller circuit current, so less mag field, so current, so less mag field, so less back e.m.f, so shorter time less back e.m.f, so shorter time for current to reach max)for current to reach max)

RL

Sketch back E.M.F vs time?Sketch back E.M.F vs time?

The back e.m.f will be The back e.m.f will be large to begin with as large to begin with as the current is the current is changing most rapidlychanging most rapidlyIt drops to zero as the It drops to zero as the rate of change of rate of change of current reduces.current reduces.Again the time Again the time constant is the time constant is the time taken to fall 63% of taken to fall 63% of max valuemax value

V

t

Vmax

Read p254 -256: Read p254 -256:

Take notes if you haven’t alreadyTake notes if you haven’t already

Do Activity 15DDo Activity 15D