Electricity (equations)

Question 1

Charge

Answer 1

Charge=CurrentTime
Q=It

S.I unit= As^-1 or C

Question 2

Current

Answer 2

Current=Charge/Time
I=Q/t

Current=Cross-sectional area * number of free elections per unit volume * charge on an electron * mean drift velocity
I=Anev

S.I unit= Cs^-1 or A

Question 3

Electromotive Force (e.m.f)

Answer 3

e.m.f= energy transferred to charge/charge
€=W/Q ~> W=€Q

S.I unit= Jc^-1 or V

Question 4

Potential Difference (p.d)

Answer 4

p.d= energy transferred to charge/charge
V=W/Q ~> W=VQ

S.I unit= Jc^-1 or V

Question 5

Resistance

Answer 5

Resistance= potential difference/current
R=V/I

S.I unit= ohm

Question 6

Resistivity

Answer 6

Resistivity= (resistance*cross-sectional area)/length of wire
P=(RA)/l

S.I unit= ohm meter

Question 7

Energy

Answer 7

Energy= powertime
E=pt

S.I unit= J

Question 8

Power

Answer 8

Power= voltagecurrent
P=VI

Power= (current)^2 *resistance
P=I^2 *R

Power= (voltage)^2 /resistance
P=V^2 /R

S.I unit= Js^-1 or W

Question 9

Work done

Answer 9

Work done= chargevoltage
W= QV

S.I unit= J

Question 10

Total Resistance

Answer 10

Total resistance
R1 + R2 + R3 +… = R

S.I unit= ohm

Question 11

Total Resistance (parallel)

Answer 11

Total resistance (parallel)
1/R1 + 1/R2 + 1/R3 +... = 1/R

S.I unit= ohm