Use this loopy starter to highlight areas you need to focus on during this revision lesson.Stop the presentation after Slide 11 - Q 10. Replay at the end of the lesson starting at Slide 12 – this 2nd set gives the answers.

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Question 1

In a telescope how is dish diameter linked to wavelength ?

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Question 2

In a pinhole camera, why does a small aperture give a sharp image, and what effect does this have on the depth of field?

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Question 3A lens has a focal length of 25 cm. What is its power?

A 0.04 dioptres

B 25 dioptres

C 4 dioptres

D Not enough information to work it out4

Question 4Which lens will produce the largest real image?

A thin concave

B thick concave

C thin convex

D thick convex

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Question 5What is the difference between a solar eclipse and a lunar eclipse, and which is rarer and why?

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Question 6

The parallax of a star is 0.5” , how far away is the star in parsecs?

angle p

Parallax angle Parallax angle can be used to calculate distance.

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Question 7Why is the parallax method only useful for finding the distance of close objects?

A they are bright enough to see

B the parallax angle is measurable

C they maintain the same position

D they have a known luminosity

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Question 8Explain the difference between intrinsic brightness (luminosity) and observed brightness.

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Question 9Why are Cepheid variable stars important to astronomers?

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Question 10The spectrum from a hot star emits:

A more intense radiation at higher frequencies

B more intense radiation at all frequencies

C very low levels in the visible spectrum

D mostly large wavelength radiation

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Question 1 answer

In a telescope how is dish diameter linked to wavelength ?

The link is larger diameters are needed for detecting longer wavelengths. Hence largest for radio waves and smallest diameters for gamma.

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Question 2 answerIn a pinhole camera, why does a small aperture give a sharp image, and what effect does this have on the depth of field? One small hole prevents overlapping images so one sharp but dim image is formed. Small apertures give a large depth of field (near and far objects equally sharp).

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Question 3 answerA lens has a focal length of 25 cm. What is its power?

C 4 dioptres

Why? To work in dioptres, distances need to be in metres.

Power = 1 ÷ focal length = 1 ÷ 0.25 m = 4

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Question 4 answerWhich lens will produce the largest real image?

C thin convex

Why? Convex lenses are converging lenses that bring parallel rays to a focal point. Thin lenses need to be further away from the screen, but produce larger images, although these are dimmer.

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Question 5 answerWhat is the difference between a solar eclipse and a lunar eclipse, and which is rarer and why?Lunar : Earth between Sun and Moon, and all aligned (so they only happen at a Full Moon).

Solar: Moon between Sun and Earth, and all aligned (so they only happen at a New Moon).

Solar are rarer as the Moon is small, so only forms a shadow on a small area of Earth. The Moon orbits around the Earth’s equator, but the Earth’s tilt affects the alignment.

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Question 6 answer

The parallax of a star is 0.5” , how far away is the star in parsecs?

Distance (pc) = 1/0.5 = 2pc

angle p

Parallax angle Parallax angle can be used to calculate distance.

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Question 7 answerWhy is the parallax method only useful for finding the distance of close objects?

B the parallax angle is measurable

Distance objects have such a small parallax angle (even measuring in arc seconds) that they are difficult to measure).

Answer A is also possible, but not the best one.

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Question 8 answerExplain the difference between intrinsic brightness and observed brightness.Intrinsic Brightness depends on temperature and size. It is how much light a star actually gives out.

Observed brightness depends on intrinsic brightness. and distance. Its how bright a star appears to an observer on Earth.

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Question 9 answerWhy are Cepheid variable stars important to astronomers?

These stars vary in brightness over a regular period. The longer the period, the brighter the Cepheid. Once the period is know, the intrinsic brightness can be inferred, and when compared to its observed brightness, you can work out very large stellar distances.

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Question 10 answerThe spectrum from a hot star emits:

A more intense radiation at higher frequencies

Why? Hot objects emit radiation from all pats of the e-m spectrum, but more in the higher frequencies / shorter wavelengths. They emit higher levels of UV, X ray and gamma and appear blue white as they emit more in this part of the visible spectrum.

Cooler red stars emit more in the red orange yellow green visible part than the blue part.

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