Common Useful Formulas

Question 1

E/Z=

Answer 1

I

(AC ohms law)

Question 2

Opposite/Hypotenuse=

Answer 2

Sin(Ø)

(Sine)

Question 3

Adjacent/Hypotenuse=

Answer 3

Cos(Ø)

(Cosine)

Question 4

Opposite/Adjacent=

Answer 4

Tan(Ø)

(Tangent)

Question 5

I_m*Sin(Ø)=

Answer 5

i

(Instantaneous current, for voltage: replace i with e and E_m)

Question 6

I_rms/Sin(45)=

Answer 6

I_m

(Max current, for voltage: replace I_rms with E_rms)

Question 7

(p*n)/120=

Answer 7

f

(Generated frequency)

Question 8

cos^-1(Adjacent/Hypotenuse)=

Answer 8

Ø

(Angle w/ cos)

Question 9

sin^-1(Opposite/Hypotenuse)=

Answer 9

Ø

(Angle w/ sin)

Question 10

tan^-1(Opposite/Adjacent)=

Answer 10

Ø

(Angle w/ tan)

Question 11

(p*mº)/2=

Answer 11

eº

(Electrical degrees, mº is mechanical degrees)

Question 12

(N²*µ*A)/l=

Answer 12

L

(Inductance)

Question 13

(k*A)/d=

Answer 13

C

(Capacitance)

Question 14

I*t=

Answer 14

Q

(Charge)

Question 15

R*C=

Answer 15

T

(Capacitive time constant)

Question 16

L/R=

Answer 16

T

(Inductive time constant)

Question 17

I*(1-e^-T)=

Answer 17

I_T

(Current at T [time constant = 1,2,3,4 or 5])

{Represents a rising value, may also be used for Voltage in a charging capacitor}

Question 18

V*e^-T=

Answer 18

V_T

(Voltage at T [time constant = 1,2,3,4 or 5])

{Represents a falling value, may also be used for Current in a (dis)charging capacitor}

Question 19

2*π*f*l=

Answer 19

X_L

(Inductive reactance)

Question 20

1/(2*π*f*C)=

Answer 20

XC

(Capacitive reactance)

Question 21

(ΔI/Δt)*L=

Answer 21

e

(Induced counter emf in a coil)

Question 22

C*V_C=

Answer 22

Q

(Charge on a capacitor)

Question 23

P/S=

Answer 23

pf

(Power factor)