The wire of the potentiometer has resistance 4 ohms and length 1 m. It is connected to a cell of e. m.f. 2 volts and internal resistance 1 ohm. If a cell of e. m.f. 1.2 volts is balanced by it, the balancing length will be:  
A)  90 cm
B)  60 cm
C)  50 cm
D)  75 cm

This is the substance(s) formed in a chemical reaction.

When the magnetic domains in a material can be aligned, but eventually drift out of alignment, the material is

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?