drawing ray diagrams

We can use ray diagrams to predict whether or not a lens will produce a useful image of an object.  The diagram is also able to predict the relative size and orientation of the image, compared to the object.

Watch these short video guides to drawing ray diagrams.

This second video shows an object more than two focal lengths away from the lens.

Finally, for an object within one focal length of the lens.

Once the ray diagram is complete, we need to describe the image that has been formed.  The description must tell us about the sizeorientation and type of image that is formed.

If the image is larger then the original object, the image is magnified
If the image is smaller than the original object, the image is diminished.

If the image is the same way up as the object, it is upright.
If the image is upside down compared to the object, it as inverted.

If the object and image are on opposite sides of the lens, it is a real image.
If the object and image are on the same side of the lens, it is a virtual image.

transit of Venus

I set my alarm clock for 4am and was disappointed to find a sky full of clouds that would prevent us from viewing the transit of Venus from Thurso and the surrounding area. 

The BBC Horizon programme broadcast last night was very good.  You can still catch it on iPlayer for the next week or download it using the link below.

booklets for all standard grade physics units

I’ve been asked to post a link to all of the booklets so that people have access to something like the energy booklet as they revise using electricity and electronics.  I’ve added these to the standard grade page now.  Look for a link called whole unit notes in each section.

For those of you who have yet to download a copy of the SQA Physics booklet, get yours here.

robot radiotherapy

Last week, the BBC broadcast a Horizon programme about new cancer treatments being trialled at the Royal Marsden Hospital in London.  The documentary followed three different types of treatment; robotic surgery, a genetically targeted drug and a radiotherapy robot.

As we’ve discovered, standard radiotherapy treatment involves splitting the required dose into 3 beams, so only cells inside the tumour receive the full dose.  The radiotherapy robot, CyberKnife, allows high energy x-rays to enter the patient’s body from many different angles.  The advantage of this robot is that it minimises the risk to healthy tissue while ensuring a fatal dose of energy is delivered to the cancer cells.

I have put together a series of clips from the programme to follow patient Ray’s treatment.  The clip from the planning meeting shows just many individual beams the robot will use during the treatment.

To find out more about how x-rays affect living cells, watch this clip from Bang Goes the Theory.

The Royal Marsden Hospital has a video that provides a quick guide to radiotherapy.

Use the download link below if you would like to save a copy of the CyberKnife video.


how satellites rule our world

BBC2 showed a really good programme about satellites last night.  This screenshot showing a satellite passing over the Highlands is taken from about 17 minutes into the show.  Click on the picture to visit the BBC’s own page about the documentary.

It was quite eye-opening to see just how much modern society relies on satellite technology.

You can download the entire programme using the link below.

ray diagram revision

We’ve reached the Space unit and are almost at the end of the course.  I showed you how to draw ray diagrams when we looked at lenses during the Health Physics unit.  Some people have asked me to repost these video clips as they were not sure how to draw ray diagrams for our telescope this morning.

Watch these clips and make sure you know the six terms we use to describe the image formed by a lens. You should be able to select three words to describe the image in your ray diagram.

how to draw a ray diagram from mr mackenzie on Vimeo.

The second video looks at a ray diagram when the object is less than one focal length away from the lens.

ray diagram for objects closer than 1f from mr mackenzie on Vimeo.

Once the ray diagram is complete, we need to describe the image that has been formed.  The description must tell us about the size, orientation and type of image that is formed.

If the image is larger then the original object, we say the image is magnified
If the image is smaller than the original object, we say the image is diminished.

If the image is the same way up as the object, we describe it is upright.
If the image is upside down compared to the object, we describe it as inverted.

If the object and image are on opposite sides of the lens, it is a real image.
If the object and image are on the same side of the lens, it is a virtual image.

electric motors

 image by explainthatstuff

We’re finishing off the electricity unit by looking at electric motors.  The page I used in class to help explain how a simple electric motor works is available here.

Here is another nice animation that shows the key parts of an electric motor.  It will stop after a few rotations but just reload the page to see it again.

Real electric motors have a few modifications;

  • they use field coils instead of a bar magnet – the field coils form a strong electromagnet when current passes through them.  The field coils do not rotate.
  • the single rotating coil is replaced by several rotating coils
  • there are more contacts on the commutator – each pair connects to a different rotating coil
  • the brushes are often made from carbon instead of metal – the carbon conducts electricity and can withstand high temperatures.  Carbon also moulds to the shape of the commutator to give a good electrical contact

image by marrrci