# EE115W4A Inductance of a Coil Sample Assignment

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.

**L _{T = }**

**L**

_{1}+_{ }L_{2 }+ L_{3 }+ L_{4….}etc.**L _{T} = 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/L _{T} = 1/L_{1} + 1/L_{2 }+ 1/L_{3} + 1/L_{4…..}etc.**

**L _{T} =1 / 1/L_{1} + 1/L_{2 }+ 1/L_{3} + 1/L_{4}**

**L _{T }= 1 / 1/ 6mH + 1/7mH + 1/9mH + 10mH**

**L _{T} = 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 I ^{2}**

**Where :**

**W = energy stored ( joules, J)**

**L = inductance (henrys, H)**

**I = current ( amps, A)**

**W = ½ ( 20mH) (3mA) ^{2}**

**W = 90 J**