Question

Identify which of the following is not a source of visible light?
A. red-hot metal
B. cool metal
C. fluorescent metal
D. the sun
E. fire

Answer 1

Hint:Electromagnetic spectrum is divided into seven regions. From the least frequency to the highest frequency. Radio waves, Microwaves, Infrared waves, Visible light, Ultraviolet rays, X-Rays and Gamma rays. Visible light also known as visible spectrum is a field of EM spectrum visible to the human eye. They have the seven colors – VIBGYOR (the rainbow colors). The seven colors come together as white color.

Complete answer:
Light is very important to every living species on earth. When atoms or molecules are excited, they enter a state which is considered as absorbing, when they relax it is considered as emitting. The electrons in the atoms get excited and are pushed into higher orbitals by the additional energy such as heat or electrical energy. When these electrons fall down, extra energy is emitted back as photons. There are different sources of visible light – natural like the sun, moon and artificial light like bulbs, tube lights.

Let’s go by all the five options and pick out the options which are not a source of visible light.
Red-hot metal is hot and therefore, it has enough energy for the electrons to get excited to higher orbitals and hence the photons are emitted when the electrons fall down. There is visible light emission.

Cool metal doesn’t have enough energy to excite an electron into higher orbitals. Hence there is no visible light.

Fluorescent metal also produces visible light. These sources involve only the vibration of electrons and not the entire body. The electrons emit some part of energy in the form of EM radiation, this type of light is known as luminescence light.

The sun is a natural source of light. A massive amount of energy is released because of nuclear fusion and this is one of the major sources of heat and light on the earth.

Fire is also a source of visible light. Fire is produced because of the chemical reaction between fuel and oxygen. The reactants have higher energy than the products. The extra energy is released as heat and light. The color of the flame depends on which material is being burnt.

Hence, the right answer is option B.

Note:Knowing the definition of visible light and how it is produced will help us solve this question. We need to remember that light is produced when electrons are excited to higher orbitals and fall down to emit electromagnetic waves which is nothing but light. Visible light helps us to make lasers, electronic devices like television, computers etc. Visible light is the most important part of the EM spectrum for us.