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A LevelPhysicsOCRExam Questions5. Newtonian World & AstrophysicsStellar Evolution

Stellar Evolution (OCR A Level Physics)

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Stellar Evolution

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Stellar Evolution

1a6 marks

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

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

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

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

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.

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

A .........................................................

B .........................................................

[1]

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3b3 marks

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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