Electricity

Question 1

What is electric charge

Answer 1

positive or negative charge

electron negative atomic nuclei

Question 2

What is electric current

Answer 2

1 Ampere = 1 coulombs per second

rate of passage of electric charge

Question 3

What sources of DC do you know?

Answer 3

Batteries

Thermocouples

Question 4

Define amperes

Answer 4

One ampere represents 6.24 x10 18 electrons per second

Question 5

What are the features of mains electricity

Answer 5

AC
50Hz
root mean square voltage of 240V
Peak voltage 340V

Question 6

What increases electrical resistance

Answer 6

increase in conductors with increased temp

decrease in semi conductors with decreased temp

increase if wire stretched and becomes longer and thinner

Question 7

What is capacitance

Answer 7

ability to hold electric charge

measured in farads

1 farad = PD of 1 volt across the plates when they charge 1 coulomb

1 plates separated by an insulator: dielectric

allow passage of AC
DC charges up but fades as capacitor becomes fully charged

Charge = capacitance x voltage (Q=CxV)
Energy stored (E) = 1/2CV2

Question 8

What influences capacitor to store charge

Answer 8

larger area
increased distance = increased charge
dielectric material

Question 9

What is inductance

Answer 9

electromotive force to be induced in a circuit by changing the current flowing in the circuit or a neighbouring circuit

induces a electromotive force proportional to the rate of change of the current

induction caused by the opening and closing of a DC circuit or continuous changing directions of an AC current

Inductance is measured in Henrys H

Block AC, pass DC

Question 10

Why is an inductor used in a defib circuit?

Answer 10

current and charge from discharging capacitor decays rapidly

inductors prolong the duration of current flow

Question 11

What is impedance?

Answer 11

Opp flow in an AC current

Sum of capacitance, inductance and resistance

Letter Z

Question 12

What is reactance?

Answer 12

Opp to flow in AC caused by inductance and capacitance rather than by resistance

Decreases with increasing current frequency

Symbol X unit Ohm

Question 13

What is a transformer

Answer 13

transform voltages up and down

Faradays law of induction: ratio of the number of coils of each circuit around the transformer core determines whether step up/down

Question 14

What is Earth

Answer 14

Electrical safety electrical connection to ground

Question 15

What is a transducer

Answer 15

Changes one form of energy to another

Question 16

Defib numbers

Answer 16

30A for 3ms with 5000V

loss within inductor
thoracic impedance 50-150 ohm (reduced after first shock)
internal defib 20-50J
biphasic 150J
monophasic 360J

Energy delivered from DC shock
E=1/2CV2
C= 100microF  V=2000V
1/2 (0.0001) x (2000)2 
=200J