Physics Revision Cards

Models of the Universe

There are two different models of the Universe.

They are:

•The geocentric model

•The heliocentric model

The geocentric model is the older of the two and was created by the ancient Greek astronomer Ptolemy. The model has the Earth at the centre.

The heliocentric model is the newer model and was created by the Polish astronomer Nicolaus Copernicus. This model has the Sun at its centre. The Church disapproved of this model. Galileo discovered four of Jupiter's moons, which showed that not all objects in space orbited the Earth.

The heliocentric model is the accepted model in modern society. 

Telescopes were invented towards the end of the sixteenth century and enabled astronomers to see objects in space in greater detail and discover new objects.

The invention of the telescope led to the discovery of four of Jupiter's moons (discovered by Galileo). Neptune, Uranus and Pluto were also discovered thanks to telescopes.

The invention of photography has allowed astronomers make more detailed observations of objects in space.

Some objects in space don't emit visible light but do emit different types of electromagnetic waves. Modern day telescopes can detect these different waves. The waves emitted are radio waves, microwaves, infrared, visible light, ultraviolet and x-rays.

Refraction occurs at the interface between two materials (E.g. Air and glass). The line at right angles to the interface is called the normal.

A convex (converging) lens is a glass block that's curved on both sides to make the lens thicker in the middle. Rays of light are brought together(converge). A convex lens focuses these rays.

The focal length of a convex lens can be found by focusing the image of a distant object onto a piece of paper.

In a refracting telescope, a convex lens (the objective lens) creates an image inside the tube which is magnified by the eyepiece lens.

Most optical devices use convex lenses to produce magnified images. The magnification depends on how curved the surface of the lens is and how close the lenses are placed.

Real images are images where the rays of light actually meet at the point where the image is seen.

Virtual images (like that seen in a mirror) is when the rays of light appear to come from an image but don't actually. Virtual images can't be shown on a screen.

Light waves are also reflected at interfaces between different materials. Whenever light passes through a lens some light is reflected, which makes the image fainter.

Refracting telescopes need large lenses to improve magnification but are heavy and difficult to make, resulting in images with distorted colours. Reflecting telescopes have a curved mirror instead of an objective lens (which is a convex lens).

The curved primary mirror focuses parallel light rays from distant objects to an image. This image is then magnified by the eyepiece.

The majority of modern telescopes are reflecting.

Transverse waves are waves which move at a 90 degree angle to the oscillation of a wave. All electromagnetic waves are transverse.

Longitudinal waves are waves where the particles move backwards and forwards in line with the direction the wave is travelling. All sound waves are longitudinal.

Wave frequency is the number of waves passing a point per second. Frequency is measured in hertz (Hz). 1 Hz = 1 wave per second.

Wavelength is the distance of two points on a wave. it can be measured at either the top (crest) or bottom (trough) of a wave. It's measured in metres.

The amplitude is the distance from the oscillation to the crest or trough. It's also measured in metres.

Wave Speed:

Wave Speed (m/s) = distance (m)

time (s)

Distance (m) = wave speed (m/s) x time (s)

Time (s) = distance (m)

        wave speed (m/s)

When there's a division in an equation, the bottom is always divided by the top.

Wavelength:

Wavelength (m) = wave speed (m/s)

    frequency (Hz)

Wave speed (m/s) = frequency (Hz) x wavelength (lambda)

Frequency (Hz) = wave speed (m/s)

  wavelength (lambda)

Remember to use the triangle method when rearranging equations to ensure you don't get mixed up.