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# Monthly Archives: February 2015

## Problem on combination of resistances

As you can see from the diagram, AD and AC are in series. Similarly, BD and BC are in series. In effect, the two series combinations are in parallel. The effective resistance of each branch (2 + 3 =5, and 3+2 =5) is 5 ohm each.  Since the resistance of each branch from D to C is 5 ohm, the current divides equally among the branches. Thus the current in each is 2.5 A.

The potential difference across, DA = 2.5 x 2 = 5 V

The potential difference across, DB = 3 x 2 = 6 V

The potential difference between A & B = 6-5 = 1 V

## Now is the time for intense study

The farewell party is over in most of the schools. Now you have to concentrate more on your studies and perform the best in the forthcoming examinations. Have a look at what you have to study and how best you can finish the work in the available time. Learn well and perform well. Wish you all the best.

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## Magnetic effect of current

A metallic wire in semicircular shape of radius 2.2m carries a current of 0.7A. What is the magnitude of the magnetic field at the centre of the semicircle?

## Mechanics Questions from Mohammed

a. Determine the work done by the motor when the wheelchair starts at rest and speeds up to its normal speed.

b. Determine the maximum distance that the wheelchair can travel on a horizontal surface at its normal speed, using its stored energy. (Ignore the energy needed for it to speed up when it starts.)

c. Suppose that 0.023 percent of the power required for driving is expended against drag due to the flexing of the wheelchair’s soft rubber tires. Calculate the magnitude of the drag force.

## Why coherent sources are required for interference?

Why coherent sources are required for interference? (Asked Poonam)