Advertisements
Advertisements
Question
How does the resistance of a wire change when:
its diameter is tripled?
Advertisements
Solution
Resistance,
`R=l/A`
where l = length of wire
A= area of cross-section of the wire
When the diameter is tripled, d' = 3d Radius, r' = 3r
Area of cross-section, `A=Api^2=A(3pi)^2=9Api^2=9A`
Thus, the area of cross-section will become nine times.
Then the new resistance,
`R'=l/A`
`R'=l/9A`
`R'=R/9`
Thus, the resistance will be reduced by nine times.
APPEARS IN
RELATED QUESTIONS
Complete the following :-
(a)
Judge the equivalent resistance when the following are connected in parallel − (a) 1 Ω and 106Ω, (b) 1 Ω and 103Ω and 106Ω.
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio `"R"/"R'"` is ______.
An electrical appliance has a resistance of 25 Ω. When this electrical appliance is connected to a 230 V supply line, the current passing through it will be:
(a) 0.92 A
(b) 2.9 A
(c) 9.2 A
(d) 92 A
Write down an expression for the resistance of a metallic wire in terms of the resistivity.
V = IRTwo resistances X and Y are connected turn by turn : (i) in parallel, and (ii) series. In which case the resultant resistance will be less than either of the individual resistances?R = R1+ R2+ R3
A p.d. of 4 V is applied to two resistors of 6 Ω and 2 Ω connected in series. Calculate:
(a) the combined resistance
(b) the current flowing
(c) the p.d. across the 6 Ω resistor
You are supplied with a number of 100 Ω resistors. How could you combine some of these resistors to make a 250 Ω resistor?
State how are the two resistors joined with a battery when equivalent resistance is more than either of the two resistances.
What potential difference is needed to drive a current o f 1 A through a 5 Ω resistor?
How will you oonnect five resistors, each of the value one ohm, to obtain an equivalent resistance of 0.2 `Omega`
When do you say that the resistors are connected in this way? Draw a circuit diagram.
Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1 A. The current through the 40 W bulb will be ______.
State expression for Cells connected in parallel.
Two resistors of 4Ω and 6Ω are connected in parallel to a cell to draw 0.5 A current from the cell. Calculate the current in each resistor.
Calculate the value of the resistance which must be connected to a 15 ohm resistance to provide on effective resistance of 6 ohm.
Two resistors having 2Ω and 3Ω resistance are connected—(i) in series, and (ii) in parallel. Find the equivalent resistance in each case.
The resistance of two resistors joined in series is 8Ω and in parallel is 1.5Ω. Find the value of the two resistances.
If R1 and R2 be the resistance of the filament of 40 W and 60 W respectively operating 220 V, then:
