Currenet Electricity (10 Numericals)

1) The power rating and voltage rating of a device are 600W, 200V Find
a) current rating b) resistance offered by the device c) energy consumed in 1 hr

Ans:
a) Power =VI
I=P/V= 3 A

b) R=V/I=200/3 ohm

c) E=Power x time=600x60x60=2160000 J

2) Two wires one of copper and other of Nichrome have same length and resistance Which wire will be thicker? Justify

Ans:
resistivity=Resistance x Area / length

since length and resistance is the same for both the wires
we can compare their area

The Nichrome wire, since an alloy will be having more resistivity ,will be thicker.

3) A 15 ohm resistance wire is cut in to 3 equal pieces and then connected in parallel across a 5V battery Find a) current through each wire b) effective resistance
 Ans:
resistance is directly proportional to length of the wire
if it is cut in to 3 equal pieces resistance of each piece will be equal to 5 ohm
effective resistance of parallel combination 

(1/R)=(1/R1)+(1/R2)+(1/R3)

then R=5/3 ohm
since it is a parallel combination the pd is same across each resistor =5V
current through each resistor is V/R1=5/5=1 A
since each resistance is same so the current through each branch is also same

a)  1 A  b) 5/3 ohm

4) Find the work done in moving 10 electrons across a potential difference of 100 V

Ans:
Q=ne

Q=10 × 6 × 10^-19 C

V=W / Q

W=Q×V

W=10 × 6 × 10^-19 × 100=6 × 10^-16

Work done=6 × 10^-16  J