10) Electric Currents

Question 1

Electric current

Answer 1

Directional movement of electric charge

Measured in amps

I=dq/dt

Question 2

Current density

Answer 2

J=di/ds

Current per unit cross sectional area of conductor

Question 3

Current density 2

Answer 3

J=zenV

J=Di/ds = d^2q/dsdt

DRAWING

Question 4

Prerequisites for the generation of electric current

Answer 4

Voltage applied between ends of conductor causing charge to move

Availability of free charge carries

Question 5

Electromotive force

Answer 5

Work of external agent for moving a positive charge along the conductor

Question 6

Conductance and resistance

Answer 6

G is conductance

R= 1/G resistance of conductor

I=GU
current = conductance x voltage

P=1/lander

Question 7

Conductance and resistance 2

Answer 7

Determined by;
Length of conductor
Cross sectional area
Material of conductor

G=lander s/L

R= p L/s

Question 8

Polar molecules

Answer 8

Positive and negative charges separated in space

Eg
Water
Salts

Question 9

Solutions of substances with polar molecules

Answer 9

The positively charged end of s polar molecule will attract the negatively charged end of another polar molecule

Question 10

Dissociation

Answer 10

The spiriting of neutral molecules into ions

Drawing

Question 11

Solvation

Answer 11

The ions obtained by dissociation are surrounded by the polar solvent molecules

Question 12

Ion diameter

Answer 12

The number of solvent molecules surrounding ion depends on temp

Question 13

Recombination

Answer 13

Bonding of ions with opposite charges to produce neutral molecules

Dynamic eq is reached between dissociation and recombination

Question 14

Dissociation constant

Answer 14

The ratio of dissociated molecules to the ratio of total number of molecules

Alpha = n+/c = n-/c

Number of ions
Number of dissolved molecules c

Depends on:
Solute conc
Temp

Question 15

Electrolytes

Answer 15

Substances with ionic conductance has positive and negative

Question 16

Mobility

Answer 16

U=v/E

Question 17

Conductivity of electrolytes

Answer 17

Conductivity depends on

Concentration, temperature and type of electrolyte

Question 18

Conductivity of biological tissue

Answer 18

Proteins and lipids have low conductivity

Blood has high conductivity

Bones and dry skin have low conductivity

Question 19

Flow of electric current though the body

Answer 19

The skin is the main resistance

Current flows via blood and lymph

Current crosses skin through pores

Question 20

Diagnostic indicator

Answer 20

Conductivity of organs is used as a diagnostic indicator

Inflammation means reduced conductivity

Increased blood supply means higher conductivity

Question 21

Conductivity of gas

Answer 21

Pure gas consists of neutral ions

They don’t contain free charge carriers

Question 22

External ionising agents

Answer 22

Ultraviolet
X rays
Gamma rays

The energy required to remove one electron from bond is ionisation

Question 23

Impact ionisation

Answer 23

When neutral atoms can become ionised when charges particles collides with it