Physics 100

Lecture 12

Generation and Distribution

of Electricity

March 5, 2018

1

Right Hand Rule #1

The magnetic field surrounding

a current-carrying straight wire

Point your right thumb in the

direction of the current

Your fingers curl around the wire

in the direction of the magnetic

field

2

Right Hand Rule #2

The magnetic field surrounding

a current-carrying coil

Curl your fingers around the coil

in the direction of the current

Your right thumb points in the

direction of the magnetic field in

the center of the coil

3

The magnet is inserted into the coil as

shown. In which direction will the

induced current flow?

4

A. Clockwise

B. Counterclockwise

C. No current will flow

The magnet is inserted into the coil as

shown. In which direction will the

induced current flow?

A. Clockwise

B. Counterclockwise

C. No current will flow

5

Generating electricity

Motors convert

electrical → kinetic energy

Generators convert

kinetic → electrical energy

Another generator animation

6

Which of the following will NOT increase

the voltage of an AC generator?

7

A. Increasing the coil wire thickness

B. Increasing the rate of coil rotation

C. Increasing the strength of the magnet

D. Increasing the number of turns in the coil

Transforming electricity

The transformer

Power is conserved

s s

p p

N V

N V

p p s sV I V I

8

The electrical distribution

system

9

More about the Grid10

V1

Vgenerate

V2

Vhome

1 2 transmitV V V I R

generate 1 transmitg gP V I V I

2

loss transmitP I R

delivered 2 transmitP V I

HotQH/t

QC/t

Cold

A power plant uses a step-up transformer

that

11

A. increases current with more secondary

windings

B. increases current with fewer secondary

windings

C. increases voltage with more secondary

windings

D. increases voltage with fewer secondary

windings

What ratio of turns Ns/N

pis needed to

reduce 120-V AC down to 9.0 V AC?

12

A. 9/120

B. 120/9

C. 120×9

D. 120

What ratio of turns Ns/N

pis needed to

reduce 120-V AC down to 9.0 V AC?

A. 9/120

B. 120/9

C. 120×9

D. 120

9 V

120 V

s s

p p

N V

N V

13

A doorbell transformer steps down from 120 V

and 0.50 A to 12 V. What is the current flow to

the doorbell?

14

A. 0.050 A

B. 6.0 A

C. 0.042 A

D. 5.0 A

A doorbell transformer steps down from 120 V

and 0.50 A to 12 V. What is the current flow to

the doorbell?

A. 0.050 A

B. 6.0 A

C. 0.042 A

D. 5.0 A

120 V 0.50 A

12 V

5.0 A

p p s s

p p

s

s

P V I V I

V II

V

15

Power Plant types

Fossil Fuel, Nuclear, Geothermal, Solar Thermal:{energy source} → Thermal energy →(via heat engine) mechanical energy →(via generator) electrical energy

Hydroelectric{solar energy brings water to high altitude} → mechanical energy →(via generator) electrical energy

18

Power Plant types

Wind turbines or wave energy plants:

{solar energy drives wind or water waves}

→ mechanical energy

→(via generator) electrical energy

Photovoltaic

{solar energy}

→(via PV cells) electrical energy

19