Advertisements
Advertisements
Question
First a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is ‘n’?
Solution
The equivalent resistance of series combination is in series with the internal resistance R of battery and in parallel combination of resistors, the equivalent resistance of parallel combination is also in series with the internal resistance of battery.
In series combination of resistors, current I is given by `I = E/(R + nR)`
Whereas in parallel combination current 10I is given by `E/(R + R/n) = 10I`
Now, according to problem,
`(1 + n)/(1 + 1/n)` ⇒ `10 = ((1 + n)/(n + 1))n`
⇒ n = 10
APPEARS IN
RELATED QUESTIONS
Calculate force per unit length acting on the wire B due to the current flowing in the wire A.(See
Figure 2 below)
A wheel with 8 metallic spokes each 50 cm long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of the Earth’s magnetic field. The Earth’s magnetic field at the place is 0.4 G and the angle of dip is 60°. Calculate the emf induced between the axle and the rim of the wheel. How will the value of emf be affected if the number of spokes were increased?
Give reason/short answer.
In the given circuit diagram two resistors are connected to a 5V supply.
Calculate potential difference across the 8Ω resistor.
Two cells of 1.25 V and 0.75 V are connected in series with anode of one connected to anode of the other. The effective voltage will be ______.
Two metal wires of identical dimensions are connected in parallel. If σ1 and σ2 are the conductivities of the metal wires respectively, the effective conductivity of the combination is
If two bulbs of wattages 25 W and 100 W respectively each rated by 220 V are connected in series with the supply of 440 v·then which bulb will fuse?
When cells are connected in parallel, then ______
Two cells of emfs E1 and E2 and internal resistances r1 and r2 respectively are connected in parallel as shown in the figure. Deduce the expression for the
- equivalent emf of the combination
- equivalent internal resistance of the combination
- potential difference between the points A and B.
The equivalent resistance of series combination of two resistors is 's'. When they are connected in parallel, the equivalent resistance is 'p'. If s = np, then the minimum value for n is ______. (Round off to the Nearest Integer)
Two cells of emf E1 and E2 and internal resistances r1 and r2 are connected in parallel, with their terminals of the same polarity connected together. Obtain an expression for the equivalent emf of the combination.
