The correct relation between current 'I' and amount of charge flown 'q' during a time 't' through a conductor is
Correct relation is current I =
⇒ q = It
The effective resistance between A and B is
6Ω is shorted so effective resistance is 4Ω.
SI unit of resistivity is
As resistivity of the material of a resistor of length l, cross-section area A and resistance R is given by :ρ = R.A/I, hence SI unit of resistivity is ohm -metre (Ω m).
A cooler of 1500 W, 200 volt and a fan of 500 W, 200 volt are to be used from a household supply. The rating of fuse to be used is
Total power used, P - P1 + P2 = 1500 + 500 = 2000 W.
Current drawn from the supply,
If four resistors each of 1Ω are connected in parallel, the effective resistance will be
If four resistors each of 1Ω are connected in parallel, the effective resistance will be 0.25Ω..
As, in parralel connection,
1/Reff. = 1/R1 + 1/R2 + ....
A fuse wire repeatedly gets burnt when used with a good heater. It is advised to use a fuse wire of
In order to get the working of heater properly, fused wire of higher rating must be used.
Resistivity of a given conductor depends on
Resistivity of a given conductor depends only on its material and the temperature. Resistivity does not depend on the dimensions of the conductor.
A coil in the heater consume power P on passing current. If it is cut into halves and joined in parallel, it will consume power
Original power consumed, P = V2/R
When used in parallel
RP = R/4
∴ New power consumed when two halves in parallel
A combination of three resistances has been shown here. Effective resistance between the points A and B is
Value of series combination of 2Ω and 2Ω resistances = 4Ω. As it is now connected in parallel to 4Ω resistance, hence the effective resistance R between the points A and B will be
If P and V are the power and potential of device, the power consumed with a supply potential V1 is
Which alloy is used to prepare the heating element of an electric iron ?
An alloy ‘nichrome’ is used to prepare the heating element of an electric iron because its resistivity is high, its melting point is high and it does not oxidise easily.
The resistance of hot filament of the bulb is about 10 times the cold resistance. What will be the resistance of 100 W-220 V lamp, when not in use ?
When the lamp is on use, it is hot.
Using joules law of heating ;
P = V2 / R
R = 2202 /100 = 484 ohm.
It is given resistance of hot lamp is 20 times the cold lamp.
Hence, R cold = 484/10 = 48.4 ohm.
Two electric lamps are rated as 220 V, 100 W and 220 V, 40 W respectively. Their electric resistances are
Resistance R = V2/P where V = voltage/potential difference and P - power
∴ electrical resistance of 100 W lamp,
and electrical resistance of 40 W lamp,
If R1 and R2 be the resistance of the filament of 40 W and 60 W respectively operating 220 V, then
For the same voltage, R ∝ 1/P
More the power, lesser the resistance.
Accordingly, R2 < R1
A wire of resistance 8Ω is bent in the form of a closed circle. What is the effective resistance between the two points A and B, at the ends of any diameter of the circle ?
When a wire of 8Ω resistance is bent in the form of a closed circle, resistance of each half (semicircular) part is 8/2 Ω = 4Ω.
As these two parts are connected in parallel across points A and B, hence effective resistance will be 2Ω.
Two resistors are connected in series gives an equivalent resistance of 10Ω. When connected in parallel, gives 2.4Ω. Then the individual resistance are
In series, Rs = R1 + R2 = 1OΩ
The rheostat is used in the circuit to :
A rheostat is used to increase or decrease the magnitude of the current flowing through a circuit without change in the voltage source.
Calculate the current flows through the 10Ω resistor in the following circuit.
In parallel, potential difference across each resistor will remain same. So, current through 10Ω resistor
The graph between current I and potential difference V in the experimental verification of Ohm’s law were drawn by four students. Which one is correct ?
I-V graph shown in figure (b) is correct because I ∝ 7.
Two Wires of same length and area, made of two materials of resistivity ρ1 and ρ2 are connected in parallel V to a source of potential. The equivalent resistivity for the same length and area is