Standard Candles (CIE A Level Physics)

Solar panels consisting of combinations of photovoltaic cells use energy in the radiation received from the Sun to generate electricity.

An advertisement for solar panels claims that the intensity of radiation from the Sun incident at the top of the Earth’s atmosphere is more than 2 kW m⁻².

Assess the validity of this claim.

Use the following data:

• radius of Sun = 6.96 × 10⁸ m
• surface temperature of Sun = 5790 K
• distance from Sun to Earth = 1.50 × 10¹¹ m

A space probe is sent on a mission from Earth to Mars.

Power for the space probe is provided by solar panels that collect radiant energy from the Sun. The solar panels have a total area of 31 m² and are directly facing the Sun throughout the journey. The efficiency of the solar panels is 30%.

The mean orbital radius of Mars about the Sun is 2.3 × 10¹¹ m.

Compare the power available to the probe when it leaves Earth's atmosphere to the power available on its arrival at Mars.

Neptune is the farthest known planet from the Sun in the Solar System. Its distance from the Sun is 30 times greater than the distance of the Earth from the Sun.

A similar space probe to the one in (b) is sent on a mission to Neptune.

Cepheids are a type of standard candle.

Describe how standard candles can be used to determine distances to stars.

Fig. 1.1 shows the light curve of a Cepheid variable star which has a radiant flux intensity on Earth of 500 nW m⁻².

Fig. 1.1

Use Fig. 1.1 to estimate the period of the Cepheid.

Fig. 1.2 shows the relationship between luminosity and period for a group of Cepheid variables.

Fig. 1.2

Use Fig. 1.2 and your answer from (b) to calculate the distance of the Cepheid from the Earth.

Luminosity of the Sun = 3.8 × 10²⁶ W