A beaker containing water is counter poised on a balance. If a finger is immersed in water so that it does not touch the bottom or the side of the beaker, the pan on which the beaker rests will:

When we dip our finger in the water, the water exerts upward thrust on the finger (Archimedes’s principle). Due to Newton’s third law of motion, the finger will exert an equal and opposite force on the water in downward direction resulting in increase of the weight of the water thus the pan moves down