Define 1 J of work

What is the change in internal energy of a system, if 10 J of heat is supplied to it and 15 J of work is done by it?

Define 1 watt of power

Define 1kg wt of force.

Explain Hallwach's and Lenard's observation on photoelectric effect. Define : a.work function b. Threshold frequency c. Stopping potential

Define work function of a metal .

Define work function. Write Einstein's photoelectric equation and explain the terms.