Turn an incandescent lamp on and off quickly while you are standing near it. You feel its thermal energy but find when you touch the bulb that it is not hot. why you felt thermal energy from it.

That was radiant energy you felt. But the outer case of the bulb (the glass envelope) did not absorb any of the radiant energy, or at least not very much.

When you turn an incandescent lamp on and off quickly while standing near it, you might feel its thermal energy even though the bulb itself doesn't feel hot to the touch. This can be explained by the process of thermal conduction and how our bodies perceive temperature.

First, let's understand how an incandescent lamp works. When electricity passes through the lamp's filament, it becomes heated to a high temperature, emitting light as a result. However, in the short period of time that you turn the lamp on and off quickly, the filament doesn't have enough time to transfer all its heat to the surrounding environment, including the bulb itself.

Now, let's talk about thermal conduction. When an object is at a higher temperature than its surroundings, it tends to transfer its heat energy to nearby cooler objects. In this case, the filament inside the incandescent lamp is at a high temperature, while the surrounding air and the bulb itself are cooler.

When you stand near the lamp and turn it on, the hot filament radiates heat energy into the surrounding air. Some of that heat is then conducted to nearby objects, including your body. This is where you feel the thermal energy.

However, when you touch the bulb, you may find that it doesn't feel hot. This is because the bulb, made of materials like glass, is not a good conductor of heat. It has a low thermal conductivity, meaning it doesn't transfer heat efficiently. As a result, the heat from the filament doesn't conduct well through the bulb material, and thus the bulb itself doesn't feel hot to the touch.

So, in summary, when you feel thermal energy from an incandescent lamp but the bulb itself doesn't feel hot, it's because the lamp's filament emits heat energy into the surrounding air, and a small portion of that heat is conducted to your body. However, the bulb's low thermal conductivity prevents the heat from transferring efficiently through the bulb, keeping it relatively cool to touch.