A LevelPhysicsOCRTopic Questions5. Newtonian World & Astrophysics5.10 Stellar Evolution

Stellar Evolution (OCR A Level Physics)

Topic Questions

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1a6 marks
a)
In 2017, an ultra-cool star TRAPPIST-1 was discovered with at least five of its own orbiting planets. Astronomers are interested about the possibility of finding life on some of the planets orbiting TRAPPIST-1.

The table below shows some data.

  TRAPPIST-1 Sun
Luminosity L/W 2.0 × 1023 3.8 × 1026
Surface temperature T/K 2500 5800
Radius of star/m R 7.0 × 108
Distance between Earth and Sun/m   1.5 × 1011
Distance between planets and TRAPPIST-1/m 1.6 × 109
to 9.0 × 109		  

The temperature T in kelvin of a planet, its distance d from the star and the luminosity L of the star are related by the expression

fraction numerator T to the power of 4 d squared over denominator L end fraction = constant

                                           

  • The average temperature of the Earth is about 290K. Explain how life may be possible on some of the planets orbiting TRAPPIST-1.
  • Use your knowledge of luminosity to show that the radius R of TRAPPIST-1 is smaller than the Sun.
  • Support your answers by calculations.

[6]

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1b3 marks
b)
Kepler’s third law can be applied to a satellite in a geostationary orbit around the Earth.

i)
Complete the equation for Kepler’s third law below.
You do not need to define any of the terms.

................. space equals space fraction numerator 4 pi squared over denominator G M end fraction space space............... 

[1]

ii)
The mass of Earth is 6.0 × 1024 kg.
Calculate the radius of the circular path of a satellite in a geostationary orbit around the Earth.

radius = .................................. m  [2]

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2a4 marks
a)
Our Sun will eventually become a red giant.

Describe and explain the next stages of evolution of our Sun.

[4]

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2b4 marks
b)
Rigel is a blue giant star in the constellation of Orion.

The table below shows some data about Rigel and about our Sun.

  Rigel Sun
Surface temperature / K   5.8 × 103
Luminosity / W 4.62 × 1031 3.85 × 1026

Wavelength of emitted light at peak intensity / nm

 240 500

 

i)
Show that the surface temperature of Rigel is 12 000 K.

[2]

ii)
Calculate the radius of Rigel.




radius = .................................... m [2]

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2c1 mark
c)
An astronomer claims to have discovered a white dwarf with a mass twice that of our Sun.

Suggest why this claim must be incorrect.

[1]

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3a1 mark

Fig. 19 is an incomplete Hertzsprung-Russell (HR) diagram of stars in our galaxy.

q19-paper-1-june-2018-ocr-a-level-physics

Fig. 19

The position of the Sun on the HR diagram is shown in Fig. 19.

a)
State the type of stars found in regions A and B.


A .........................................................
B .........................................................
[1]

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3b3 marks
b)
The Sun is a main sequence star. Its surface temperature is 5800 K. The wavelength of the emitted light at maximum intensity is 550 nm.

Beta Pictoris is also a main sequence star. The wavelength of the emitted light at maximum intensity from this star is 370 nm.

i)
Calculate the surface temperature of Beta Pictoris.

temperature = ...................................................... K [2]

 

ii)
On Fig. 19, mark the likely position of Beta Pictoris with a letter P.

[1]

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