+-

The moment this switch is closed

energizing this electromagnet

time

we expect the current jumps from zero to

I = V/R

time switchis closed

+-

However… as each coil of thiselectromagnetstarts to pull

current

its contribution to the magnetic fieldshoves flux down the center of all the neighboring coils.

each resists with an induced voltageto slow this change down...

a small voltage countering the battery.

+-

Which means the current ramps up!

time

We reach the full current V/R only after a few moments:

I = V/R

time switchis closed

Current winds through the inductor as shown, creating an electromagnet with its North Pole on its

1) right end.

2) left end.

3) top surface.

4) bottom surface.

+-

A light bulb is run by a battery in series with an inductor.

When the switch is opened, current

1) stops abruptly.

2) gradually dies out.

3) continues flowing until

the

bulb cools.

4) reverses direction,

returning

charge to the battery.

+-

A light bulb is run by a battery in series with an inductor.

When plugged into an active household outlet, which of the light bulbs above will be brighter?

1) A

2) B

3) both the same

Self-Induction in Daily Life When you turn off your toaster by unplugging it

current changes rapidly to zero rapidly changing B field produced very large voltage induced in toaster’s wires spark

If you unplug your computer while it is

still turned on, large voltages

may be generated, possibly destroying

the CPU chip.

voltage difference large enough for electrons to flow through air

+

e

+++ +

- -- -

+ ++ +

- -- -

Equilibrium position …antenna current zero..

+

- The electric field in this region points:

A. up.B. down.C. into the screen.D. out of the screen.

E field points down

E field points up

E field momentarily zero

E field points down

E field points up

E field zero

strong

weak

zero

E-fieldpointingdown

Also, this OSCILLATION generates a B-Field!

slowing to zero speed

maximum speed

As this positive chargemoves up, the B-fieldin this region pointsINTO the screen

slowing to zero speed

Also, this OSCILLATION generates a B-Field!

maximum speed

As this positive charge moves up,the B-field in this

region pointsINTO the screen

B field is oscillating, continuously flipping the magnetic field

in & out & in & out & in & out & · · ·

E field is oscillating, continuously flipping the electric field

and at the same time…

up & down & up & down & up & down & · · ·

c is used to stand for the “speed of light”

Before the days of cable, television sets often had two

antennae on them, one straight, and one

circular.

One antenna picked up electric field

oscillations, and the other picked up

magnetic field oscillations.

Which antenna picked up the magnetic oscillations?

1) the circular antenna

2) the straight antenna

Amplitude Modulation

Carrier Frequency

Frequency Modulation

The loss of flux induces a current in the coil to partially replace the sudden loss. Though it soon fades, this current continues to flow in the same direction as the current from the battery had.

QUESTION 1

QUESTION 2

The inductor slows down sudden changes …even the fluctuations of AC current!This means with the inductor in place, the AC current never makes itto quite as high as maximum values (before reversing direction) whenwith the inductor. the rms average current is also lower then, soI2R, the power consumed in the light-bulb is much less!

QUESTION 3

QUESTION 4

QUESTION 5

Electric field lines point away from the positive charge, into the negative. At the moment pictured, the field right of the antenna points UP (see next slide).

Set up to monitor the local magnetic fields…whenever the magnetic field passing through this circular loop CHANGES, a current is induced in it.

1) right end.

2) gradually dies out.

One more example of induction easing sudden changes.

2) B

A. up.

1) the circular antenna

This is the type of antenna (see slide 23) your radio probably uses to pick up FM stations.