2009 General Studies, all questions
UPSC Prelims 2009 · General Studies
Question 118: Science and Technology
Which one among the following has the highest energy ?
aBlue light
bGreen light
cRed light
dYellow light
AnswerThe answer is (a).
The energy of a photon is E = h x frequency, so the colour with the highest frequency (shortest wavelength) carries the most energy. In the visible spectrum, going from red to violet, frequency rises: red, yellow, green, blue. So among the four options, blue light has the highest energy. Red has the lowest energy of the four.
Why each option is right or wrong
- (a) Right: blue has the highest frequency of the four.
- (b) Green has a lower frequency than blue.
- (c) Red has the lowest frequency and energy.
- (d) Yellow has a lower frequency than blue.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2009, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.