Chap 11: Electric Current and Its Measurement

Question 1

magnitude of electric currents are

Answer 1

• the quantities of current
• short form: electric current
• represented by l
• unit: Ampere (A, s= milliampere mA, s= microampere µA)

Question 2

to measure electric current

Answer 2

Ammeter
* symbol: —A—
* labelled: A, mA, µA
* connected in series only
* three connecting leads & two measuring ranges
* current comes: +, current out: -
* smallest division → values of current

the electric current tested shouldnt exceed measuring range, it would be damaged

Question 3

how to see if the heart is working properly

Answer 3

electrocardiogram
(ECG or EKG)

Question 4

detects the changes in electricity in human body

Answer 4

lie detector
* smallest electric current: 1 mA
* lose muscle control: 15 mA
* lethal: 100 mA

Question 5

voltage

Answer 5

• “potential difference”
• represented by V
• unit: volt (V, l= kilovolt kV, s= millivolt mV)
• electric source creates a driving force, voltage is the driving force of electric source to form an electric current
• voltage → electric source = electric current (Ampere)
• driving force of a battery towards free electrons is directional

1 V = 10’3 mV

1 kV = 10’3 V

Question 6

to measure electric current

Answer 6

Voltmeter
* symbol: —V—
* unit: kV, V, mV
* connected in parallel only
* fixed measuring range
* three connecting leads & two measuring ranges
* smallest division = different voltages for different measuring range
* positive electrode: + terminal, negataice electrode: - terminal

Question 7

organisms that produce electricity

Answer 7

bioelectricity
electric eel

Question 8

Resistance

Answer 8

slowing down a conductor
* represented by R
* unit: ohm (Ω, l=kiloohm kΩ, l=megaohm MΩ)

Question 9

conductors

Answer 9

• conduct electricity easily: charges moves freely from one place to another
• metals, graphite, human body, earth, aqueous solutions
• free electrons: electrons that can escape from the attractive forces of the atoms and move from one place to another

Question 10

insulators

Answer 10

• do not conduct electrivity easily: charges are all restricted within the atom
• rubber glass, porcelain, plactic, oil

Question 11

semiconductors

Answer 11

• dractic changes in conductivity when there is a change in
  -illumination (light)
  -temperature
  -impurities added
• if oxidized or corroded → conducting abilities are reduced
• e.g: satellites needs to be gold plated, diodes and transistors
• wafers: diodes, transistors, resistors

Question 12

superconduction
* sudden disappearance of resistance:
* substances that reduces their resistances:
* temperature when it turns from a normal to a superconducting condition:

Answer 12

• sudden disappearance of resistance: superconduction phenomenon
• substances that reduces their resistances: superconductors
• temperature when it turns from a normal to a superconducting condition: transition temperature