Solar radiation emitted by sun resembles that emitted by a black body at a temperature of 6000 K. Maximum intensity is emitted at wavelength of about 4800 Å. If the sun were to cool down from 6000 K to 3000 K, then the peak intensity would occur at a wavelength

4800 Å
9600 Å
2400 Å
19200 Å

Solution

The rate of radiation of a black body at 0ºC is E joule per sec.Then the rate of radiation of this black body at 273ºc will be

16 E
8 E
4 E
E

Solution

According to Stefan’s Law

energy radiated per sec E = σAT⁴

(heree = 1 for black body)

for first case E = σ A(273)⁴

for second case E₁=σA(546)⁴ so E₁=16E

A metal ball of surface area 200 square cm, temperature 527ºC is surrounded by a vessel at 27ºC. If the emissivity of the metal is 0.4, then the rate of loss of heat from the ball is approximately \(\sigma =5.67\times 10^{-8}\frac{joule}{m^{2}\times sec\times k^{2}}\)

108 joule
168 joule
182 joule
192 joule

Solution

A cylindrical rod of aluminium is of length 20 cms and radius 2 cms. The two ends are maintained at temperatures of 0ºC and 50ºC the coefficient of thermal conductivity is \(\frac{0.5\, cal}{cm\times sec\times ^{\circ}C}\) Then the thermal resistance of the rod in \(\frac{cal}{sec\times ^{\circ}C}\) is

318
31.8
3.18
0.318

Solution

Steam is passed into 22 gm of water at 20ºC. The mass of water that will be present when the water acquires a temperatue of 90ºC (Latent heat of steam is 540 cal/g)is

24.83 gm
24 gm
24 gm
30 gm

Solution

Let m be the mass of steam condensed. Then

m × 540 + m × 10/2 = 22 × 70

∴ m = 2.83 gm

Now,total mass= 22 + 2.83 = 24.83 gm

A metallic bar is heated from 0ºC to 100ºC. The coeficient of linear expansion is 10^-5 K^-1. What will be the percentage in crease in length?

0.01%
0.1%
1%
10%

Solution

If a bar is made of copper whose coefficient of linear expansion is one and a half times that of iron, the ratio of force developed in the copper bar to the iron bar of identical lengths and cross-sections, when heated through the same temperature range (Young’s modulus of copper may be taken to be equal to that of iron) is

Solution

A pendulum clock is 5 seconds fast at temperature of 15ºC and 10 seconds slow at a temperature of 30ºC. At what temperature does it give the correct time? (take time interval =24 hours)

18ºC
20ºC
22ºC
25ºC

Solution

Δt = ¹⁄₂ α ΔT × t

∴ 5 = ¹⁄₂ α (T - 15) × 86400

and 10 = ¹⁄₂ α (30 - T) × 86400

A metallic rod l cm long, A square cm in cross-section is heated through tºC. If Young’s modulus of elasticity of the metal is E and the mean coefficient of linear expansion is α per degree celsius, then the compressional force required top revent the rod from expanding along its length is

E A α t
E A α t/(1 + α t)
EA α t/(1 – α t)
E l α t

Solution

\(E=\frac{F/A}{\Delta \iota /\iota }=\frac{stress}{strain}\)where Δl=(l'–l) =lαt so F= EAαt

The resistance of a resistance thermometer has values 2.71 and 3.70 ohms at 10ºC and 100ºC respectively. The temperature at which the resistance is 3.26 ohm is

40ºC
50ºC
60ºC
70ºC

Solution

R_t = R₀(1 + α t)

2.71 = R₀(1 + α × 10) ... (1)

3.70 = R₀ (1 + α × 100) ... (2)

3.26 = R₀ (1 + α t) ... (3)

Solve these equations to obtain the value of t.

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