Question

Q1) An electric iron consumes energy at a rate of 840W ehen heating is in at maximum and 360W when heating is at minimum. The voltage is 220V. What are current and resistance in each case?

Q2) Which uses more energy, a250W set in 1hour OR a 1200W toaster in 10 minutes?

Q3) What is the role of split rings in DC motor?

Q4) Write the principal of generator?

Q5) Write the function of brush in generator?

Answer 1

1) When heating at max rate,

Power, P = 840W

Voltage, V = 220V

We know P = VI

⇒ 840 = 220 × I

⇒ I = 840/220

⇒ I = 4 A

R = V/I = 220/4 = 55 Ω

So current = 4A and resistance = 55Ω

When heating at minimum rate,

power, P = 360W

V = 220V

We know P = VI

⇒ 360 = 220 × I

⇒ I = 360/220

⇒ I = 1.636 A

R = V/I = 220/1.636 = 134.45 Ω

So current = 1.636A and resistance = 134.45Ω

2)

For T.V set

Power (P) = 250w, Time (t) = 1hr=60×60=3600s

For Toaster

Power (P) = 1200w, Time (t) = 10min=10×60=600s

We know that Energy (E) = P×t

∴ Energy consumed by a TV set = 250 × 3600 = 9 × 10⁵J

∴ Energy consumed by a toaster = 1200 × 600 = 7.2× 10⁵J

∴ the energy consumed by a 250 W TV set in 1 h is more than the energy

consumed by a toaster of power 1200 W in 10 minutes.

3) Split rings are used to change the polarity of current after every half rotation so as to make the motor move continuously in same direction

4)An electric generator works on the principle of electro magnetic induction ie,when a conductor which is placed inside a magnetic field moves,an EMF will be induced in the conductor and moves through the conductor in the direction as specified by Fleming's right hand rule.

5)The function of brushes is to make contact with the rotating rings and through them to supply current to the coil.

Thank you :)