Physics Quiz on Resistors and Mirrors

If two resistors of 25Ω and 15Ω are joined together in series and then placed in parallel with a 40Ω resistor, the effective resistance of the combination is :

• 0.1Ω

• 10Ω

• 20Ω

• 40Ω

If this arrangement of three resistors was to be replaced by a single resistor, its resistance should be :

• 9Ω

• 4Ω

• 6Ω

• 18Ω

The potential difference across the 3Ω resistor is :

• 19 V

• 12 V

• 1 V

• 2 V

A battery and three lamps are connected as shown. Which of the following statements about the currents at X,Y and Z is correct ?

• The current at 𝑍 is greater than that at 𝑌

• The current at 𝑌 is greater than that at 𝑍

• The current at 𝑋 equals the current at 𝑌

• The current at 𝑋 equals the current at 𝑍

V1,V2 and V3 are the p.ds. across the 1Ω,2Ω and 3Ω resistors in the following diagram, and the current is 5 A. Which one of the columns (𝑎) to (d) shows the correct values of 𝑉1,𝑉2 and 𝑉3 measured in volts ?

• 1.0, 2.0, 3.0

• 5.0, 10.0, 15.0

• 5.0, 2.5, 1.6

• 4.0, 3.0, 2.0

A wire of resistance R1 is cut into five equal pieces. These five pieces of wire are then connected in parallel. If the resultant resistance of this combination be 𝑅2, then the ratio 𝑅1/𝑅2 is :

• 125

• 15

• 5

• 25

An electric bulb is rated 220 V and 100 W . When it is operated on 110 V , the power consumed will be :

• 100 W

• 75 W

• 50 W

• 25 W

An electric kettle for use on a 230 V supply is rated at 3000 W . For safe working, the cable connected to it should be able to carry at maximum :

• 2 A

• 5 A

• 10 A

• 15 A

At a given time, a house is supplied with 100 A at 220 V . How many 75 W, 220V light bulbs could be switched on in the house at the same time (if they are all connected in parallel)?

• 93

• 193

• 293

• 393

David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m . If he moves 1 m towards the mirror, then the distance between David and his image will be :

• 3 m

• 5 m

• 6 m

• 8 m