Radiations coming from the Sun are mostly in the form of
- (a)light only.
- (b)light and long wavelength infrared.
- (c)light and short wavelength infrared.
- (d)both short and long wavelength infrared.
Correct — C, light and short wavelength infrared. The Sun's surface is very hot (about 5800 K), so its radiation peaks in the visible band and most of its energy comes out as visible light together with near-infrared, i.e. SHORT-wavelength infrared (plus some ultraviolet). This is called shortwave solar radiation. The far cooler Earth, by contrast, re-radiates energy as LONG-wavelength (far) infrared.
- (a)light only. — The Sun emits well beyond the visible - a large part of its energy is infrared and some is ultraviolet. 'Light only' ignores the substantial near-infrared component.
- (b)light and long wavelength infrared. — Long-wavelength (far) infrared is what the cool Earth emits, not the hot Sun. The Sun's infrared is mostly SHORT-wavelength (near) infrared, because hotter bodies radiate at shorter wavelengths (Wien's law).
- (d)both short and long wavelength infrared. — The Sun's output is dominated by short-wavelength (near) infrared alongside visible light; long-wavelength infrared is only a minor part. This option overstates the long-infrared share and leaves out visible light, the main component.
The Sun behaves as a blackbody at about 5800 K. By Wien's law its emission peaks in the visible range (around 500 nm), and most of its energy is spread across visible light plus near-infrared (short-wavelength infrared), with some ultraviolet. This 'shortwave' solar radiation contrasts with the 'longwave' far-infrared that the cooler Earth re-emits.
The key is the Sun's high temperature: hotter bodies radiate at shorter wavelengths. So the Sun's radiation is mainly visible light with short-wavelength infrared, not the long-wavelength infrared that the much cooler Earth gives off. That distinction (shortwave Sun versus longwave Earth) points straight to option (c).
- The Sun's surface is about 5800 K; its radiation peaks in the visible range (around 500 nm).
- Solar radiation is mostly visible light plus near-infrared (short-wave), with some ultraviolet.
- Hotter bodies radiate at shorter wavelengths (Wien's displacement law).
- The cooler Earth re-emits energy as long-wave (far) infrared - the basis of the greenhouse effect.
- Swapping shortwave (the Sun) and longwave (the Earth) infrared.
- Thinking the Sun emits 'light only' - a large share of its output is infrared.
Solar radiation is asked as 'the Sun emits mostly...' or through the shortwave / longwave (Sun versus Earth) distinction.
No directly related past PYQ was found.
- practice — not a real PYQ
The radiation emitted by the Earth's surface is mostly in the form of
- (a)visible light
- (b)short-wave infrared
- (c)long-wave infrared
- (d)ultraviolet
Answer(c) long-wave infrared - the Earth is far cooler than the Sun.
- practice — not a real PYQ
According to Wien's law, as the temperature of a body increases, the wavelength of its maximum emission
- (a)increases
- (b)decreases
- (c)stays constant
- (d)becomes infinite
Answer(b) decreases - hotter bodies radiate at shorter wavelengths.