Question

Figures 1 to 3 show the working of a simple A.C. generator. Study the diagrams and answers of the following questions.

(i) State and explain the principle underlying the working of a simple generator. 

(ii) Where is the loop of wire placed? 

(iii) What happens when the loop is rotated? 

(iv) Indicate the direction of the current flow through the wire for the first half of the turn (Figure 1). Name and state the rule used in finding the direction of the current. 

(v) Indicate the direction of the current for the case shown in figure 2. 

(vi) Indicate the direction of current in the outer circuit (i.e., electric bulb) in figure 1 and in figure 3. 

(vii) What type of current is shown in the above diagrams? Explain.

Answer 1

(i) The generator works on the principle of Electromagnetic Induction. Whenever the flux passing through a closed circuit changes, e.m.f. is induced in it and a current begins to flow. Its direction is given by Fleming’s Right Hand Rule or Lenz Law. As long as the loop is moving within the magnetic field an electric current will flow. 

(ii) The loop of wire is placed between the two poles of a ‘U’-shaped magnet. 

(iii) When the loop of wire is rotated between the two poles of a ‘U’-shaped magnet an electric current flows through the wire. 

(iv) As rotation of the coil is the clockwise direction and the direction of magnetic field is from right to left, the current will flow in the anticlockwise direction, i.e., from B₂ and B₁. The law used is Lenz’s law. 

Lenz’s law: “The direction of the induced e.m.f. is such that it opposes the change responsible for its production.” 

(v) No electric current flows when the loop of wire is halfway through the turn, i.e., at an angle of 90° [as sin 90° = 0.] 

(vi) Figure 1: From brush B₂ to B₁ 

Figure 3: From brush B₁ to B₂ 

(vii) The type of current shown is an alternating current or A.C. current. When the loop of wire makes the second half of the turn (fig., the direction of the electric current through the bulb is reversed and it flows back in the opposite direction.