Question

Flash light equipped with a new set of batteries, produces bright light. As the batteries wear out:
A. The light intensity gets reduced with no change in its colour
B. Light colour changes first to yellow and then red with no change in intensity
C. It stops working suddenly while giving while giving white light
D. Colour changes to red and also intensity gets reduced

Answer 1

Hint: We studied batteries, its uses and working in physics. We can solve this problem with the concept of current electricity and the battery working. A battery is a device which stores the chemical energy and converts it to the electrical energy. When the current flows through the wire due to discharging of the battery, the temperature of the filament increases which is responsible for colour change of light.

Complete step by step answer:
The chemical reactions in the battery involve the flow of electrons which provides an electric current that can be used to do work. Charged ions also flow through an electrolyte solution to balance the flow of the electrons. Different electrodes produced different reactions that affect how the battery works.

The colour of visible light depends upon the wavelength because each colour has different wavelength but the wavelength depends upon the temperature of the object emitting radiation so the colour of the light also depends upon the temperature.

In the discharging of the battery , the current decreases, heat produced by the filament also decreases hence the temperature also decreases resulting in the change in the colour of wire to red and the intensity also gets reduced.

So, the correct answer is “Option D”.

Note:
We also use the temperature and wavelength relationship (given by Wien’s displacement law i.e. temperature and wavelength has inverse relationship) in the question. Each colour has a different wavelength. When all the waves are seen together, they make white light. Red has the longest wavelength while the violet has the shortest wavelength.