Question

Q3() Explain the function of a capacitor and resistor in an electronic device. You may choose a device which has both electrical components, or separate devices for each component. (5 marks) (b) 632.8 nm is incident on a Monochromatic light from a helium-neon laser of 2. diffraction grating containing 6000 lines/em. Analyse the number of bright fringes that can be observed. (2 marks) Calculate the angle for each bright fringe that occur. (3 marks)

Answer 1

Here I have explained the use of a capacitor and resistor in an electric fan

Capacitor:  There is a single phase induction motor in most of the fans. In order to rotate the motor there must be resulting magnetic field(which will create the necessary torque to rotate the motor). In fans, magnetic field is created by stator winding. This magnetic field is positive in half cycle and negative in the other half. Which gives zero net magnetic field over a cycle, hence torque is also zero.

When we add a capacitor to the additional auxiliary winding of stator, it creates a magnetic field which leads the main winding field by 90 degrees.Thus we end up with two fields which are at 90 degrees to each other, creating a rotating field responsible for the start of the motor.

Resistor:

In order to control the speed of fans, resistors are used. These resistors are called blower resistor. The fan speed can be changed by changing the resistance of blower resistor. The change in resistance then limits the current through the motor, which dictates the speed at which the blower fan works.

(b) the dix fons between slite, da 1 6o ou cm 1.67x10-6 how from the formula dsino = na --(I) n dsino for n to be maximum Sine! d 1.67x10-6 a 632.8 x 10 2.639 which is less than 3 hence nurt bos ar fringes obzexvdE2 (ii) W ongle for first fringe be e, then E =) Sine, a eqn (1) d sine, 632.8 d 1.6776 → Sin e, = 0.3789 85,- 22.269 angle for second fringe be Oz then eqh (i) ² d Sine, = 2.) => Sin@= 21 28632.8; d Sinen = 0.7578 → O2 = 49.27°) 1.6 TXH

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