حرارتی طبیعیات

Written by Dr. Hamza Farooq (Physics)

نیٹ · طبیعیات · 5 سوالات

نام: ____________________ تاریخ: ____________

What is the maximum efficiency of an engine working between 600 K and 300 K?
- A 50%
- B 100%
- C 75%
- D 25%
The power radiated by a hot body is proportional to its absolute temperature raised to the power of:
- A 3
- B 2
- C 4
- D 1
A sealed rigid container of gas is heated from 27 degrees C to 327 degrees C. By what factor does the pressure change?
- A It doubles
- B It becomes 12 times larger
- C It does not change
- D It halves
A gas expands at a constant pressure of 1 x 10⁵ Pa, and its volume increases by 2 x 10⁻³ m³. How much work does it do?
- A 2000 J
- B 100 J
- C 50 J
- D 200 J
A 1 m metal rod lengthens by 1.2 mm when its temperature rises by 100 degrees C. What is its coefficient of linear expansion?
- A 1.2 x 10⁻⁷ per degree C
- B 1.2 x 10⁻³ per degree C
- C 1.2 x 10⁻⁵ per degree C
- D 1.2 x 10⁻² per degree C

جوابی کلید

1. A, 2. C, 3. A, 4. D, 5. C

Carnot efficiency = 1 - 300/600 = 0.5, which is 50%.
This is the Stefan-Boltzmann law: power is proportional to T⁴.
The temperatures are 300 K and 600 K. At constant volume the pressure is proportional to absolute temperature, so it doubles.
Work = P x change in volume = 10⁵ x 2 x 10⁻³ = 200 J.
alpha = change in length / (length x temperature change) = 1.2 x 10⁻³ / (1 x 100) = 1.2 x 10⁻⁵ per degree C.