A simple apparatus to detect whether my ear touches a metal plate lying on the floor
If you really want to make contact with the skin of your ear, I'm afraid you're out of luck. 

The problem is that, if you make contact to the plate with your ear, all of the bulb current must flow through your skin, and skin resistance is usually high enough that a 3-volt bulb will not get enough current to light for any reasonable supply voltage. Here, for instance is a flashlight bulb for sale, and it draws 0.86 amps. Even if you were soaking wet (good workout, right?) with a skin resistance of 1000 ohms, $$ i(current) = \frac{V(volts)}{R(resistance)}$$ so you'd need 860 volts. On the one hand, you wouldn't need to be able to see the bulb to know that you'd made contact with the plate. On the other hand, you'd be unconscious and wouldn't know you'd made contact with the plate. Well, actually you'd probably be dead.

If you still want to try this setup, you could always make a clamp that would attach a wire to your ear, and make contact with the plate with the clamp. In this case a 3-volt battery would work fine and there would be no danger of shock. For that matter, depending on what piercings you have in your ears already the whole thing might be pretty easy. Your circuit would look like







simulate this circuit &ndash; Schematic created using CircuitLab

When the clamp (held by the ear) touches the plate, the bulb will light up. 

As a plus, if you don't have any existing piercings to repurpose as contacts, any clamp which will stay in place will be pretty uncomfortable, and this will inspire you to do your pushups quickly.