Resistors Combination – Numerical Problem

What is the effective resistance between P and Q in the diagram?


Asked Malik Ahmed

Answer : 8 ohms

The Two arms have resistances 32 ohm and are in parallel, Their effective resistance is 1 ohms. This is in parallel with the middle arm. So the effective resistance is 8 ohms.



The three arms have resistances 32, 1 and 32 respectively and are in parallel. Therefore, taking their reciprocals and adding will give the answer.


How supercooled water is prevented from turning into ice?

Water below zero degree celsius is called super cooled water. liquid water does not become completely unstable as it becomes supercooled, prior to turning into ice crystals. an energy barrier for crystal formation exists throughout the region in which supercooled water’s compressibility continues to rise.

Read more at:


Focal length of convex mirror using convex lens

It is given that the image formed by the convex mirror should be at radius of curvature . Why it should?




I guess that the question is based on the experiment to determine the focal length of a convex mirror using convex lens.

Initially a convex lens is used to obtain a real image of a candle. (or pin if you are doing the experiment using the optical bench) Then a convex mirror is kept in such a way that the image is obtained on the same position as the object. This happens when the rays are incident normal to the mirror. The rays of light incident normal to the mirror are directed towards the centre of curvature. Since the image was formed by the rays which are now reflected normally, the distance between the convex mirror and the original position of image gives the radius of curvature.

Experiment for focal length of convex lens

See the diagram for illustration.