Week 6

Question 1

Telescope Collecting area

Answer 1

Bigger area = can collect more photons

Question 2

Focusing device

Answer 2

• depends on wavelength
  visible = curved mirror
  x-ray = nested mirror

Question 3

Detector

Answer 3

records photons, visible

Question 4

Einstein’s Theory of Special Relativity relies on what 2 principles

Answer 4

1. The laws of physics are the same for everyone

2. The speed of light is measured by everyone to be the same

Question 5

Lunar eclipse

Answer 5

Earth passes between the Sun and the Moon, so that Earth’s shadow passes across the Moon

Question 6

solar eclipse

Answer 6

Moon passes between Earth and Sun blocking out the Sun

Question 7

what kind of telescopes are used on earth?

Answer 7

optical and radio (some infrared)

Question 8

Effects of Earth’s Atmosphere

Answer 8

most wavelengths of light are filtered out, optics can alter image (effect of seeing)

Question 9

What affects telescope resolution?

Answer 9

Size of the collecting area, Wavelength of light, atmosphere/ionosphere

Question 10

Special relativity

Answer 10

describes the motion of one object relative to another, when both are moving with constant velocity

Question 11

General relativity

Answer 11

Acceleration feels like gravity

Question 12

consequences of special relativity

Answer 12

• Time dilation (fast clocks tick slower)
• Relativity of simultaneity (order of events)
• Length contraction (fast objects appear to shrink)
• Mass increase (fast objects gain mass)

Question 13

Reference frames

Answer 13

Measured velocity depends on frame of reference, There is no such thing as a stationary frame of reference

Question 14

inertial frame of reference

Answer 14

moving at constant velocity

Question 15

Accelerated frame of reference

Answer 15

accelerating or in a gravitational field

Question 16

Why can’t we reach the speed of light?

Answer 16

• All observers must see light travelling a c, and you moving more slowly
• Thus you cannot accelerate to a velocity greater than or equal to the speed of light

Question 17

Time dialation

Answer 17

Time appears to pass more slowly as you move faster

Question 18

Consequences of general relativity

Answer 18

• Space and Time are linked as spacetime
• Time Dilation due to gravity
• Gravity is curved spacetime
• Black Holes
• Tests: GPS, Orbits and Gravitational Lenses

Question 19

Curved spacetime

Answer 19

Spacetime in the presence of masses is curved

Question 20

Equivalence principle

Answer 20

-gravitational acceleration and acceleration due to a
force produce the same effect
-You cannot tell the difference between being in a
closed room on Earth, and in a closed room in space accelerating

Question 21

Gravitational Lensing

Answer 21

Matter capable of bending the light from the source as the light travels towards the observer due to curved space time

Question 22

Gravitational waves

Answer 22

‘ripples’ moving at the speed of light in the fabric of space-time, Generated by lopsided, moving masses

Question 23

In 2030, the Australian Space Agency launches a spaceship to our nearest neighbour Alpha Centauri (4 lightyears away).

How long will the journey take according to a clock on the spaceship if it travels at v=0.999 c=299482km/s (where ‘c’ is the speed of light equal to 299782km/s).

Answer 23

Just over 2 months.

Question 24

If the Sun was shrunk to fit the same mass into a smaller volume what would happen to the curvature of spacetime near the surface of the Sun?

Answer 24

decrease volume + same mass = density increases,

which causes spacetime curvature to increase

Question 25

Would would happen to Spacetime at the surface of the Sun if you kept the volume the same but increased the mass?

Answer 25

increase mass + same volume = density increases,

which causes spacetime curvature to increase

Question 26

Einstein’s Theory of General Relativity is based around the principle that gravity is indistinguishable from what?

Answer 26

acceleration

Question 27

light and intense gravitational field

Answer 27

A light ray is bent more by an intense gravitational field.

Question 28

GR tell us that clocks run slower in a gravitational field. If you take two clocks, one on the surface of Earth, and one orbiting 100km above, and check what time they say a year later what would you see?

Answer 28

The clock on earth will run slower, as clocks run slower in intense gravitational fields, and the stength of gravity increases as you get closer to the surface on the Earth,

Question 29

Curvature Near Black Hole

Answer 29

radius keeps reducing