AC generator and transformer — practice questions

Question 1 · difficulty L1 · recall

An AC generator converts

• A. mechanical energy into electrical energy
• B. electrical energy into mechanical energy only
• C. heat directly into magnetic flux
• D. DC into chemical energy

Question 2 · difficulty L1 · understanding

The basic principle of an AC generator is

• A. electrostatic shielding
• B. electromagnetic induction
• C. Ohmic heating
• D. radioactive decay

Question 3 · difficulty L2 · understanding

A power transmission line feeds input power at $$2.3 \mathrm{~kV}$$ to a step down transformer with its primary winding having 3000 turns. The output power is delivered at $$230 \mathrm{~V}$$ by the transformer. The current in the primary of the transformer is $$5 \mathrm{~A}$$ and its efficiency is $$90 \%$$. The winding of transformer is made of copper. The output current of transformer is _________ $$A$$.

Question 4 · difficulty L2 · understanding

An ideal transformer with purely resistive load operates at $$12 ~\mathrm{kV}$$ on the primary side. It supplies electrical energy to a number of nearby houses at $$120 \mathrm{~V}$$. The average rate of energy consumption in the houses served by the transformer is 60 $$\mathrm{kW}$$. The value of resistive load $$(\mathrm{Rs})$$ required in the secondary circuit will be ___________ $$\mathrm{m} \Omega$$.

Question 5 · difficulty L2 · understanding

A square shaped coil of area $$70 \mathrm{~cm}^{2}$$ having 600 turns rotates in a magnetic field of $$0.4 ~\mathrm{wbm}^{-2}$$, about an axis which is parallel to one of the side of the coil and perpendicular to the direction of field. If the coil completes 500 revolution in a minute, the instantaneous emf when the plane of the coil is inclined at $$60^{\circ}$$ with the field, will be ____________ V. (Take $$\pi=\frac{22}{7}$$)

Question 6 · difficulty L2 · understanding

In an ac generator, a rectangular coil of 100 turns each having area $14 \times 10^{-2} \mathrm{~m}^{2}$ is rotated at $360 ~\mathrm{rev} / \mathrm{min}$ about an axis perpendicular to a uniform magnetic field of magnitude $3.0 \mathrm{~T}$. The maximum value of the emf produced will be ________ $V$. $\left(\right.$ Take $\left.\pi=\frac{22}{7}\right)$

Question 7 · difficulty L2 · understanding

A common transistor radio set requires 12 V (D.C.) for its operation. The D.C. source is constructed by using a transformer and a rectifier circuit, which are operated at 220 V (A.C.) on standard domestic A.C. supply. The number of turns of secondary coil are 24, then the number of turns of primary are ___________.

Question 8 · difficulty L2 · understanding

Primary coil of a transformer is connected to $$220 \mathrm{~V}$$ ac. Primary and secondary turns of the transforms are 100 and 10 respectively. Secondary coil of transformer is connected to two series resistances shown in figure. The output voltage $$\left(V_0\right)$$ is :

• A. 7 V
• B. 44 V
• C. 22 V
• D. 15 V

Question 9 · difficulty L2 · understanding

Primary side of a transformer is connected to $$230 \mathrm{~V}, 50 \mathrm{~Hz}$$ supply. Turns ratio of primary to secondary winding is $$10: 1$$. Load resistance connected to secondary side is $$46 \Omega$$. The power consumed in it is :

• A. 11.5 W
• B. 12.5 W
• C. 10.0 W
• D. 12.0 W

Question 10 · difficulty L2 · understanding

Match List - I with List - II : List I List II A. AC generator I. Presence of both L and C B. Transformer II. Electromagnetic Induction C. Resonance phenomenon to occur III. Quality factor D. Sharpness of resonance IV. Mutual Induction Choose the correct answer from the options given below :

• A. A-II, B-I, C-III, D-IV
• B. A-IV, B-III, C-I, D-II
• C. A-II, B-IV, C-I, D-III
• D. A-IV, B-II, C-I, D-III