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Heat and Thermodynamics question

2023 · Shift 1 · Q49
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Heat and Thermodynamics question

2023 · Shift 1 · Q49

JEE AdvancedPhysicsHeat and ThermodynamicsMCQ+3 / −1
Match the temperature of a black body given in List-I with an appropriate statement in List-II, and choose the correct option.

[Given: Wien's constant as 2.9×10−3 m−K2.9 \times 10^{-3} \mathrm{~m}-\mathrm{K}2.9×10−3 m−K and hce=1.24×10−6 V−m\frac{h c}{e}=1.24 \times 10^{-6} \mathrm{~V}-\mathrm{m}ehc​=1.24×10−6 V−m]

List - I List - II
(P) 2000 K2000 \mathrm{~K}2000 K (1) The radiation at peak wavelength can lead to emission of photoelectrons from a metal of work function 4eV4 \mathrm{eV}4eV.
(Q) 3000 K3000 \mathrm{~K}3000 K (2) The radiation at peak wavelength is visible to human eye.
(R) 5000 K5000 \mathrm{~K}5000 K (3) The radiation at peak emission wavelength will result in the widest central maximum of a single slit diffraction.
(S) 10000 K10000 \mathrm{~K}10000 K (4) The power emitted per unit area is 1/161 / 161/16 of that emitted by a blackbody at temperature 6000 K6000 \mathrm{~K}6000 K.
(5) The radiation at peak emission wavelength can be used to image human bones.
  1. A
    P→3,Q→5,R→2,S→3P \rightarrow 3, Q \rightarrow 5, R \rightarrow 2, S \rightarrow 3P→3,Q→5,R→2,S→3
  2. B
    P→3,Q→2,R→4,S→1P \rightarrow 3, Q \rightarrow 2, R \rightarrow 4, S \rightarrow 1P→3,Q→2,R→4,S→1
  3. C
    P→3,Q→4,R→2,S→1P \rightarrow 3, Q \rightarrow 4, R \rightarrow 2, S \rightarrow 1P→3,Q→4,R→2,S→1
  4. D
    P→1,Q→2,R→5,S→3P \rightarrow 1, Q \rightarrow 2, R \rightarrow 5, S \rightarrow 3P→1,Q→2,R→5,S→3
View written solutionFree

Correct answer: C

  1. Use Wien’s displacement law

For a black body,

λmax⁡T=2.9×10−3 m K\lambda_{\max} T = 2.9 \times 10^{-3}\ \text{m K}λmax​T=2.9×10−3 m K

So,

λmax⁡=2.9×10−3T\lambda_{\max} = \frac{2.9\times 10^{-3}}{T}λmax​=T2.9×10−3​

Let us compute for each temperature.

  • (P) T=2000 KT=2000\,\text{K}T=2000K

    λmax⁡=2.9×10−32000=1.45×10−6 m=1450 nm\lambda_{\max} = \frac{2.9\times 10^{-3}}{2000}=1.45\times 10^{-6}\,\text{m}=1450\,\text{nm}λmax​=20002.9×10−3​=1.45×10−6m=1450nm

    This is in the infrared region.

  • (Q) T=3000 KT=3000\,\text{K}T=3000K

    λmax⁡=2.9×10−33000=9.67×10−7 m=967 nm\lambda_{\max} = \frac{2.9\times 10^{-3}}{3000}=9.67\times 10^{-7}\,\text{m}=967\,\text{nm}λmax​=30002.9×10−3​=9.67×10−7m=967nm

    This is also infrared.

  • (R) T=5000 KT=5000\,\text{K}T=5000K

    λmax⁡=2.9×10−35000=5.8×10−7 m=580 nm\lambda_{\max} = \frac{2.9\times 10^{-3}}{5000}=5.8\times 10^{-7}\,\text{m}=580\,\text{nm}λmax​=50002.9×10−3​=5.8×10−7m=580nm

    This lies in the visible region.

  • (S) T=10000 KT=10000\,\text{K}T=10000K

    λmax⁡=2.9×10−310000=2.9×10−7 m=290 nm\lambda_{\max} = \frac{2.9\times 10^{-3}}{10000}=2.9\times 10^{-7}\,\text{m}=290\,\text{nm}λmax​=100002.9×10−3​=2.9×10−7m=290nm

    This is ultraviolet.


  1. Match with statement (3): widest central maximum in single slit diffraction

For a single slit,

angular width of central maximum∝λ\text{angular width of central maximum} \propto \lambdaangular width of central maximum∝λ

So the largest wavelength gives the widest central maximum.

Among all temperatures, the largest λmax⁡\lambda_{\max}λmax​ is for 2000 K.

Hence,

P→3P \rightarrow 3P→3
  1. Match with statement (4): power emitted per unit area is 1/161/161/16 of that at 6000 K6000\,\text{K}6000K

Using Stefan–Boltzmann law,

E∝T4E \propto T^4E∝T4

We need

(T6000)4=116\left(\frac{T}{6000}\right)^4 = \frac{1}{16}(6000T​)4=161​

Taking fourth root,

T6000=12\frac{T}{6000} = \frac{1}{2}6000T​=21​

So,

T=3000 KT=3000\,\text{K}T=3000K

Thus,

Q→4Q \rightarrow 4Q→4
  1. Match with statement (2): radiation at peak wavelength is visible to human eye

Visible range is approximately

400 nm to 700 nm400\,\text{nm} \text{ to } 700\,\text{nm}400nm to 700nm

From above,

  • 1450 nm1450\,\text{nm}1450nm: not visible
  • 967 nm967\,\text{nm}967nm: not visible
  • 580 nm580\,\text{nm}580nm: visible
  • 290 nm290\,\text{nm}290nm: not visible

Hence,

R→2R \rightarrow 2R→2
  1. Match with statement (1): peak radiation can emit photoelectrons from a metal of work function 4 eV4\,\text{eV}4eV

For photoelectric emission,

hν≥ϕh\nu \ge \phihν≥ϕ

or

hcλ≥4 eV\frac{hc}{\lambda} \ge 4\,\text{eV}λhc​≥4eV

Given,

hce=1.24×10−6 V m\frac{hc}{e}=1.24\times 10^{-6}\,\text{V m}ehc​=1.24×10−6V m

Thus photon energy in eV is

E=1.24×10−6λ eVE = \frac{1.24\times 10^{-6}}{\lambda}\ \text{eV}E=λ1.24×10−6​ eV

For (S), λ=2.9×10−7 m\lambda=2.9\times 10^{-7}\,\text{m}λ=2.9×10−7m:

E=1.24×10−62.9×10−7≈4.28 eVE = \frac{1.24\times 10^{-6}}{2.9\times 10^{-7}} \approx 4.28\,\text{eV}E=2.9×10−71.24×10−6​≈4.28eV

Since 4.28>44.28>44.28>4, photoemission is possible.

Hence,

S→1S \rightarrow 1S→1
  1. Check statement (5): can be used to image human bones

Imaging bones requires X-rays, which have much smaller wavelengths than UV/visible/IR. None of the peak wavelengths except certainly not 5000 K5000\,\text{K}5000K correspond to X-rays. So statement (5) is not used.


  1. Final matching

Thus the correct matching is:

P→3,Q→4,R→2,S→1P \rightarrow 3,\quad Q \rightarrow 4,\quad R \rightarrow 2,\quad S \rightarrow 1P→3,Q→4,R→2,S→1

This corresponds to Option C.

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