greater the objective lens,greater the magnification
and the length of the telescope depends on the objective

The objective lens controls how much light is collected. Since most binocular object are large and dim, the light gathering ability is the crucial variable. Also, if you are holding the binoculars with your hands (rather than on a mount), it is difficult to have enough stability for the larger magnifications. Anything over 10x should be mounted. Astronomical binoculars should have objective lenses of at least 50mm. I have found that magnification has some effect, but not nearly as much as many beginners think it will. In a choice between 7×50 and 10×50, the 10×50 will have a larger image and so some extra detail will be possible. On the other hand, some objects are too big to fit into the field of view of 10×50s. A good pair of 7×50s are wonderful for bright comets!

What you really want is to get the brightest looking view possible, which requires making the exit pupil of the binoculars as close as possible to the same size as your eye's pupil, which in the dark is usually about 7mm. The exit pupil size of any binoculars is the objective diameter divided by the magnification. So for 7×50 it is 7.14mm, pretty close to 7.

Just chiming in to agree with mathematician's excellent answer. Prakash doesn't have clue what he's talking about….the size of the objective has nothing to do with magnification.

Hey, Prakash, it's the FOCAL LENGTH of the objective, not the diameter, that partly determines the magnification.