Option 1 states that when an incandescent electric bulb glows, the electric energy is completely converted into light energy. This option is not entirely accurate. While the main purpose of an incandescent bulb is to produce light, it does not convert all the electric energy into light energy. Instead, a significant portion of the electric energy is also converted into heat energy. This is due to the nature of the filament in the bulb, which becomes extremely hot when electricity passes through it, emitting both light and heat.

Option 3 suggests that the light energy is converted into electric energy. This is incorrect because the flow of energy in an incandescent bulb is from the electrical source to the bulb, resulting in the conversion of electrical energy into light and heat energy. There is no conversion of light energy back into electrical energy within the bulb.

Option 4 states that the electric energy is converted into magnetic energy. This is also incorrect because an incandescent bulb does not generate a substantial amount of magnetic energy. The primary energy outputs of an incandescent bulb are light and heat.

Therefore, the correct answer is option 2, as it correctly states that when an incandescent electric bulb glows, the electric energy is partly converted into light energy and partly into heat