## Basic Electrical Engineering (BEE) - Jun 2015

### First Year Engineering (Semester 1)

TOTAL MARKS:

TOTAL TIME: HOURS

### Answer any one question from Q1 and Q2

**1 (a)** If a coil of 150 turns is linked with a flux of 0.01 Wb when carrying a current of 10 A, then calculate the induced emf.

i) if this current is uniformly reversed in 0.1 second.

(ii) if this current is interrupted in 0.05 second.(6 marks)
**1 (b)** Define insulation resistance and obtain an expression for insulation resistance of a single core cable.(6 marks)
**2 (a)** Explain what do you mean by statically induced EMF and dynamically induced EMF(6 marks)
**2 (b)** A coil of insulated copper wire has a resistance of 150 Ω at 20°C. When the coil is connected across a 240 V supply, the current after several hours is 1.25 A. Calculate the temperature of the coil, assuming the temp. co-efficient of resistance of 20°C to be 0.0039 per °C.(6 marks)

### Answer any one question from Q3 and Q4

**3 (a)** Derive an EMF equation of 1-ph transformer.(6 marks)
**3 (b)** Derive an expression for instantaneous current and power
consumed when voltage of V = V_{m} sin ( t) is applied to pure inductance alone. Also draw the phasor diagram.(6 marks)
**4 (a)** A single phase 4 kVA transformer has 400 turns on its primary and 1000 secondary turns. The net cross-sectional area of the core is 60 cm^{2}. When the primary winding is connected to 500 V, 50 Hz supply, calculate:

i) the max. value of flux density in the core

(ii) the voltage induced in the secondary winding and

(iii) the secondary full load current.(6 marks)
**4 (b)** The expression of the alternating current is given by i = 5.48 sin Ωt:

Calculate:

(i) the average value

(ii) RMS value of the current

(iii) power consumed if the current is passed through a resistance of 10 Ω.(6 marks)

### Answer any one question from Q5 and Q6

**5 (a)** What is admittance of an AC circuit ? What are its two
components? State units of these quantities. How the admittance is expressed in rectangular and polar form?(6 marks)
**5 (b)** An impedance Z_{1} = (100 + j0) Ω is connected in series with another impedance Z_{2} = (50 + j80) . The circuit is connected to a single phase 230 V, 50 Hz supply. Calculate:

i) current drawn by the circuit

(ii) power consumed by whole circuit

(iii) circuit power factor.(7 marks)
**6 (a)** Draw and explain phasor diagram of an RLC series circuit,
When :

i) X_{C} > X_{L}.

ii) X_{C} < X_{L}

iii) X_{C} = X_{L}(7 marks)
**6 (b)** A delta connected balanced load across a 400 V 3-phase supply consist of three identical impedances, each equal to (15+j12) Ω Find the line current, active power and reactive power.(6 marks)

### Answer any one question from Q7 and Q8

**7 (a)** State and explain Superposition Theorem.(6 marks)
**7 (b)** Using Kirchhoff's Law, determine the current flowing through 6 &Omelga; resistance.

(7 marks)
**8 (a)** Derive the expressions to convert delta connected resistances into equivalent star circuit.(6 marks)
**8 (b)** Using Thevenin's Theorem, determine the value of current flowing through 6 Ω resistance.

(7 marks)