(a) Use the thin-lens equation to derive an expression for q in terms of f and p. (b) Prove that for a real object and a diverging lens, the image must always be virtual. Hint: Set f 5 2u f u and show that q must be less than zero under the given conditions. (c) For a real object and converging lens, what inequality involving p and f must hold if the image is to be real?

Chapter 2 Notes When mass is at an equilibrium and the spring is stretched in equilibrium the force of gravity balances the elastic force from a spring. The elastic force depends on the elongation of our string F= -kx Where x is elongation and k is the stiffness or spring constant. K depends on thickness of the wire as well as on the material our spring is made of. Please note the minus sign in the formula. It demonstrates that elastic force is always directed against elongation trying to bring the suspended mass back to equilibrium point. This kind of force is called restoring force, and its presence is necessary for the existence of any vibration When the string is stretched and the mass is released, the restoring force becomes larger then the force