1. Calculate the inductance of a coil that induces 120V when the current through it changes at a rate of 5A/s.
L = VL/(di /dt)
120V/5A/s = 24 H
2. Calculate the inductance of a coil that induces 850V when the current through itchanges at a rate of 30mA in 2µs.
L = VL/(di/dt)
850V/ (30mA/2µs )= 0.05667H = 56.66 mH
3. Given an iron core with 200 turns, a length of 0.35m and an area of 3x10-4m2,determine the inductance.
N = 200 turns
l = 0.35m
A = 3*10-4m2
L = (N2* A/l) * 1.26µ1* (2002* 3*10-4/ 0.35) * 1.26µ = 4.32 µH
4. A 10:1 transformer has NP= 300, VP= 240V and IP= 2A. Determine NS, VS, and Is.
Ns= 300 / 10 = 30 turns
Vs= 240V / 10 = 24 V
Is= Vs/R1= 24V / 10/Ip= 24V / 5 = 4.8A
5. Four inductors of values 6mH, 7mH, 9mH, and 10mH are connected in series. Determine the total inductance.
LT = L1+ L2 + L3 + L4….etc.
LT = 6mH + 7mH + 9mH + 10mH = 32mH or 0.032H
6. Four inductors of values 6mH, 7mH, 9mH, and 10mH are connected in parallel. Determine the total equivalent inductance.
1/LT = 1/L1 + 1/L2 + 1/L3 + 1/L4…..etc.
LT =1 / 1/L1 + 1/L2 + 1/L3 + 1/L4
LT = 1 / 1/ 6mH + 1/7mH + 1/9mH + 10mH
LT = 1.92073170mH or 1920.73170µH
7. Calculate the energy store in a 20mH inductor with a current of 3mA flowing through it.
W = ½ L I2
W = energy stored ( joules, J)
L = inductance (henrys, H)
I = current ( amps, A)
W = ½ ( 20mH) (3mA)2
W = 90 J
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