Question

Give reason : why the terminal voltage is less than the emf of a cell

Answer 1

cells has their internal resistance, which causes voltage drop,.
so if cell's emf is E ,internal resistance is r and
terminal voltage is v.when current I is flowing from cell ,its terminal voltage is v=E - Ir .is <E

Answer 2

ANSWER:-

Because emf is the potential difference across the two terminals of a voltage source when it is not connected to any circuit. And once it is connected to a circuit, the voltage reduces slightly because of the internal resistance of the voltage source.