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 cord of a frog could generate muscular spasms throughout its body. Luigi Galvani ( )

Mary Shelley ( ) 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 ( )

Electromotive series Carbon Gold Silver Copper Tin Lead Iron Zinc Both tend to dissolve in even a salt solution! though often dilute sulphuric acid was used… ZINC Cu MORE NEGATIVE MORE POSITIVE The zinc electrode collects a positive charge as it dissolves. As deposits collect on the copper electrode it develops a positive charge.

Zinc can Manganese dioxide Carbon core Cardboard bitumen washer insulating sleeve Deteriorating zinc canister builds negative charge at base of this dry cell

1.5 volts 1.5 volts 3.0 volts You probably already know, from replacing batteries in common devices: Batteries chained end-to-end add their potential differences.

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

An automotive accumulator is a 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 to dissolve into the acid - - A constant voltage is 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-e- The amount of charge passing any given point per second is the current: 1 Coul sec = 1 Ampere

Georg Simon Ohm ohm (  ) allows a current of 1 ampere to pass when a potential difference of 1 volt is applied across it. V  I V = 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)  (3) 32  (2) 25.6  (4) 40 

Work is continuously being performed within 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 = WORK TIME 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? 1) the 25 W bulb 2) the 100 W bulb 3) the same for both Which carries the greater current? 1) the 25 W bulb 2) the 100 W bulb 3) the same for both

A 1440 W microwave oven is designed to operate using a 120 V power source. What is the resistance of this appliance? 1) 0.1  2) 10  3) 72  4) need to know the current 5) none of these

Current Effect Fatal? Current Effect Fatal? Ampere mild shock no Ampere painful shock no <0.010 Ampere tingles no Ampere paralysis of motor muscles no Ampere threshold of pain ( cannot let go !)no breathing becomes laboredno Ampere breathing becomes laboredno Ampere death due to fibrillation seconds Ampere death due to fibrillation seconds Ampere no fibrillation, but severe seconds Ampere no fibrillation, but severe seconds burns and breathing stops burns and breathing stops >0.200 Ampere heart stops seconds >0.200 Ampere heart stops seconds Ampere serious burns instantly Ampere serious burns 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 A QUESTION 1 (4) 40  QUESTION 2 (5) 600 Watts QUESTION 3 P = IV Greater resistance: (1) the 25 W bulb QUESTION 4 Since P = V 2 /R, P  1/R. QUESTION 5 The greater current: (2) 100 W bulb The bulb with the smallest resistance must draw the greater current! Also: since P = IV, P  I. (2) 10  QUESTION 6