Physics Unit 7 Test

• 550°C

• 450°C

• 400°C

• 500°C

If a bulb has a 20W power. If it is working at 60% efficiency, then its output power is

• 12W

• 15W

• 20W

• 18W

Which of the following has a negative temperature coefficient?

• C

• Mn

• Fe

• Ag

P_out will be maximum when

• R>r

• R=r

• R<r

• None of these

The terminal voltage in the presence of the current would be

• Less than the emf by I_r

• Greater than emf by I_r

• Equal to emf by I_r

• Zero

A battery whose emf is 40 V has an internal resistance of 5 Ω. If this battery is connected to a 15 Ω resistor R, what will be the voltage drop across R?

• 10 V

• 30 V

• 15 V

• 40 V

An electric iron is marked 20 volts 500 W. The units consumed by it in using it for 24 hours will be            :

• 12

• 24

• 5

• 1100

A circuit diagram is shown in which we have three resistances. Among three which develops maximum power?

• R₁

• R₂

• R₃

• in series power remains same

The V-I graph of a conductor at two different temperatures as shown in Fig. The relation between resistance will be

• R₁ > R₂

• R₁ = R₂

• R₂ > R₁

• R₁ = 2 R₂

Length of two wires of same material have ratio 2:3 and their radii have the ratio 1:2 Then the ratio of their resistances is

• 1 : 3

• 4 : 3

• 1 : 6

• 8 : 3