While cutting a frog leg, Galvani's steel scalpel touched a brass hook that was holding the leg in place.

The leg twitched.

A charge applied to the spinal cordof a frog could generate muscular

spasms throughout its body.

Luigi Galvani(1737-1798)

Mary Shelley (1797-1851)

wrote “Frankenstein”(1816)

In 1799 Volta made his 'Voltaic Cell' by alternating disks of copper and zinc

separated by salt-water moistened pads.

Alessandro Giuseppe Antonio Anastasio Volta

(1745-1827)

Electromotive seriesCarbonGoldSilverCopperTinLeadIronZinc

Both tend to dissolve in even a salt solution!though often dilute sulphuric acid was used…

−+ +→ eZnZn 22

ZINC Cu

MO

RE

NE

GA

TIV

E

MO

RE

PO

SIT

IVE

The zinc electrodecollects a positive charge as it dissolves.

As deposits collect on the copper electrodeit develops a positive charge.

Zinc canManganesedioxide

Carbon coreCardboard

bitumen

washer insulating sleeve

Deteriorating zinc canister builds negative charge at base of this dry cell.

+ + ++ +

- -- -- -

1.5volts

1.5volts

3.0volts

You probably already know,from replacing batteries in

common devices:

Batteries chainedend-to-endadd their potential

differences.

The word “battery” actually means aset of “cells” lined up in sequence:

An automotive accumulator isa battery of 6 2-volt lead-acid cells.

A plate coated in brown lead dioxide deposits (built while “recharging”) builds a positive charge when dissolved in dilute sulphuric acid. Grey lead plates grow negative as lead sulphate coating develops.

Every e that leaves the zinc electrode and

enters the “circuit”

enables another ion todissolve into the acid

-

-

A constant voltageis maintained

(as long as the Zn and Cu lasts).

So unlike a single discharge, this source is continuous!

+ + + - - -

- --

+

-

“Conventional current”or just “current”

I

e-

The amount of charge passing any given point

per second is the current: t

QI

ΔΔ=

1 Coulsec

= 1 Ampere

Georg Simon Ohm1789 - 1854

1 ohm () allows a current of 1 ampere to pass when a

potential difference of 1 volt is applied across it.

V IV = IR

An electric toaster element (Nichrome) is 20.

How great is the current when it is connected to a 120v line?

Ohm’s Law: V = IR

(1) 1/6 A (4) 6 A (2) 1 A (5) 120 A (3) 5 A (6) 240 A

0.8A runs through a lamp when attached to a 32v source.

What is its resistance?

(1) 0.025 (3) 32 (2) 25.6 (4) 40

Work is continuously being performedwithin a battery (or generator)

to maintain steady current flow!

Through friction /atomic collisions with the crystal lattice of the resistor

the supplied energy is converted to heat.

(if hot enough may even produce light!)

How rapidly is work being done in an electrical circuit?

POWER = WORKTIME

What electrical unit is most closely associated with work (energy)?

What electrical unit involves time?

What is the unit of POWER?

If an electric iron draws 5 Amperes from a 120v line,

at what rate is it using power?

(1) 6 Watts (2) 12 Watts(3) 120 Watts (4) 240 Watts(5) 600 Watts (6) 720 Watts

Which has a greater resistance, a 100 Watt lightbulb or a 25 Watt lightbulb?Which has a greater resistance, a 100 Watt lightbulb or a 25 Watt lightbulb?

1) the 25 W bulb1) the 25 W bulb

2) the 100 W bulb2) the 100 W bulb

3) the same for both3) the same for both

Which carries the greater current?Which carries the greater current?

1) the 25 W bulb1) the 25 W bulb

2) the 100 W bulb2) the 100 W bulb

3) the same for both3) the same for both

A A 1440 W1440 W microwave oven is microwave oven is

designed to operate using a designed to operate using a

120 V120 V power source. What is power source. What is

the resistance of this appliance?the resistance of this appliance?

1) 0.1 1) 0.1

2) 10 2) 10

3) 72 3) 72

4) need to know the current 4) need to know the current 5) none of these5) none of these

CurrentCurrent Effect Effect Fatal?Fatal?

0.001 Ampere mild shock no

0.005 Ampere painful shock no

<0.010 Ampere tingles no

0.010 Ampere paralysis of motor muscles no

0.020 Ampere threshold of pain (cannot let go!) no

0.030 Ampere breathing becomes laboredbreathing becomes labored nono

0.100 Ampere 0.100 Ampere death due to fibrillationdeath due to fibrillation seconds seconds

0.200 Ampere no fibrillation, but severe seconds0.200 Ampere no fibrillation, but severe seconds

burns and burns and breathing stopsbreathing stops

>0.200 Ampere heart stops>0.200 Ampere heart stops seconds seconds

1.000 Ampere serious burns1.000 Ampere serious burns instantly instantly

Galvani was correct in so far as our central nervous system is in fact

a complex electrical circuit:

Neurons fire electrical pulses along synapses.Muscle fibers contract in response to these signals.

(4) 6 AQUESTION 1

(4) 40 QUESTION 2 Ampvolts 8.0/32

(5) 600 WattsQUESTION 3 P = IV

Greater resistance: (1) the 25 W bulbGreater resistance: (1) the 25 W bulb

QUESTION 4 Since P = V2/R, P 1/R.

QUESTION 5

The greater current: (2) 100 W bulbThe greater current: (2) 100 W bulbThe bulb with the smallest resistance must draw the greater current!Also: since P = IV, P I.

(2) 10 (2) 10 QUESTION 6

=101440/)120( 2 WV