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## Monday, May 2, 2011

### Solved Electricity numerical for class 10

Question: Two bulbs have ratings 100 W, 220 V and 60 W, 220 V respectively. Which one has a greater resistance?
Answer: P=VI=  V2/R For the same V, R is inversely proportional to P. Therefore, the bulb 60 W, 220 V has a greater resistance.

Question: A torch bulb has a resistance of 1 Ω when cold. It draws a current of 0.2 A from a source of 2 V and glows. Calculate
(i) the resistance of the bulb when glowing and
(ii) explain the reason for the difference in resistance.

Answer: (i) When the bulb glows:
V = I R ---- Ohm's law R = V/I = 2/.2 =10 Ω
(ii) Resistance of the filament of the bulb increases with increase in temperature. Hence when it glows its resistances is greater than when it is cold.

Question: Calculate the resistance of 1 km long copper wire of radius 1 mm. (Resistivity of copper = 1.72 x 1 0-8

Answer: L = 1 km = 1000 m
R = 1 mm = 1 x 1 0-3
A = p r2

Question: When a potential difference of 2 V is applied across the ends of a wire of 5 m length, a current of 1A is found to flow through it. Calculate: (i) the resistance per unit length of the wire (ii) the resistance of 2 m length of this wire (iii) the resistance across the ends of the wire if it is doubled on itself.

Answer: (i) V = I R ----- Ohm's law

(ii) Resistance of 2 m length of the wire = 0.4 x 2

(iii) When the wire is doubled on itself:
(1) the area of cross-section is doubled. If A is the original C.S. area, now it is 2 A.
(2) The length becomes half i.e.

#### 1 comment:

pearls of wisdom said...

it was very usesfull
I just need someone to help me with how i should approach this question. I have NO idea how i should solve it please help!
Two identical particles, each having charge +q, are fixed in space and separated by a distance d. A third point charge -Q is free to move and lies initially at rest on the perpendicular bisector of the two charges a distance x from the midpoint between the two fixed charges.
the question is b) How fast will the charge -Q be moving when it is at the midpoint between the two fixed charges, if initially it is released at a distance a<<d from the midpoint?
pls try to send reply soon to -ishwaryasun@gmail.com