Black-body radiationEdexcel A-Level Physics: Subtopic test

1. 1
   The interior of a furnace is held at a constant temperature of 1500 K. Engineers model the furnace interior as a black-body radiator.

   (a)

   Which statement describes a black body?

   [1 mark]

   • AAny object that appears black in visible light
   • BAn object that emits radiation only at one wavelength
   • CAn object that absorbs all electromagnetic radiation incident on it and emits a continuous spectrum that depends only on its temperature
   • DAn object that reflects all electromagnetic radiation incident on it

   (b)

   Calculate the wavelength at which the furnace interior emits most intensely.

   [1 mark]

   • A1.93 × 10⁻⁶ m
   • B5.18 × 10⁵ m
   • C4.35 m
   • D1.93 × 10⁻³ m

   (c)

   The temperature of the furnace interior is raised to 1800 K. State and explain two ways in which the radiation curve of the furnace changes.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A star has a constant radius while its surface temperature rises from 5000 K to 10 000 K. Treat the star as a black body.

   (a)

   By what factor does the luminosity of the star change as its surface temperature rises from 5000 K to 10 000 K?

   [1 mark]

   • A2
   • B4
   • C8
   • D16

   (b)

   What happens to the peak wavelength of the radiation emitted by the star over the same change?

   [1 mark]

   • AIt doubles
   • BIt halves
   • CIt decreases to one quarter
   • DIt stays the same

   (c)

   Explain why the star appears bluer when its surface temperature is 10 000 K than when it is 5000 K.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The Sun radiates approximately as a black body. The wavelength at which it emits radiation most intensely is 5.0 × 10⁻⁷ m, and its radius is 7.0 × 10⁸ m.

   (a)

   Calculate the surface temperature of the Sun.

   [3 marks]

   (b)

   Calculate the luminosity of the Sun.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Astronomers study two stars, P and Q, each approximated as a black body. Star P has a surface temperature of 3000 K and a radius of 7.0 × 10¹⁰ m. Star Q has a surface temperature of 6000 K and a radius of 7.0 × 10⁸ m.

   (a)

   Describe and explain how the radiation curves of star P and star Q differ. Include the peak wavelength of each star.

   [6 marks]

   (b)

   Determine the ratio of the luminosity of P to the luminosity of Q, and explain why the cooler star has the greater luminosity.

   [6 marks]

   Total for question 4: 12 marks

End of questions