# Recent Changes

### Monday, October 17

1. Electricity edited ... {Static Electricity written questions 1.pdf} Two of the same charge i.e. positive and positi…
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{Static Electricity written questions 1.pdf}
Two of the same charge i.e. positive and positive or negative and negative, repel each other (exert a 'push' force). Once again, the size of the force is bigger for a bigger sized charge and at a closer distance.
Either{water_bending.jpg}
Either
a positive
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force on ansome types of uncharged object e.g. a balloon that has been rubbed to charge ite.g.rubbed pen can make a streamattract bits of paper. It can also attract water bend towards it:
as shown in the picture.
Something
that has
Remember that electrons are negative.
objects that have a surplus of electrons will be negatively charged
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Magnetism and electromagnetism
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termed ferromagnetic, andand are attracted
Iron is the best known magnetic substance, but nickel, cobalt, various alloys and the oxide of iron known as ferrite or magnetite are all capable of being attracted to magnets or made into magnets.
The attractive force produced by a magnet is due to a magnetic force field we will discuss in more detail later.
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(notes in preparation, use text in the interim)
{right_hand_grip_rule.png}
Electromagnetism
A wire carrying an electric current has a magnetic field around it. The direction of the field is shown in the picture: The field lines are circles that run anticlockwise if the current is coming towards you. The other way to think of it is that the field lines go in the direction that your fingers curl if you hold the wire with your right hand and your thumb pointing in the direction of the current. This is called the "right hand grip rule".
{wire_compasses.png}
A compass placed on the piece of paper illustrated would have its needle pointing in the directions of the field lines at that point.
The magnetic field is strongest close to the wire and reduces in direct proportion to the linear distance.
Magnetic field strength is given in units called tesla. The symbol for tesla is T. A field of one tesla is extremely strong; even a rare earth magnet has a field of only a few millitesla at the strongest.
The magnetic field strength is calculated using the formula
{tesla_formula.png}
In this formula, B is the magnetic field strength in tesla; I is the current in amps and d is the perpendicular distance from the wire in metres.
The "k" in this formula is a constant Constants are things that are needed in formulas to make the answer come out in the right size and units for a particular situation. For example,. you have used the formula F = mg to calculate the force on an an object of mass m due to gravity. The value of g we use is 9.8 N kg-1. This value is approximate and is only true for Earth; it would be different on Mars. The units for g (of ) are needed to make the answer come out in newtons.
In the magnetic field formula the constant k stands for a constant that only applies in air or a vacuum; it would have a different value in different situations. The value of the constant is k = 2 x 10-7 T m A-1. The units of this are the units needed to make the answer come out in tesla if you use current in amps and distance in metres. Note that an alternative way of writing this is k -2 x 10-7 T N A-2.; this would give you an answer in N A-1 m-1 (which is actually another way of writing tesla). This is similar to the way that the constant "g" can be written as g = 9.8 N kg-1 or g = 9.8 m s-2 , They are mathematically equivalent but written in different ways.

Review of this unit
Electricity workbook: note you must be logged into your SHC Google account for this link to work. Can I suggest you download the PDF and load it up either into your own Google Drive folder or into an external application you can use to write on it e.g. Notability (Apple)
(view changes)
3:58 pm
2. 3:45 pm
3. 3:38 pm
4. 3:32 pm
5. 3:27 pm

### Thursday, September 15

1. earth physics edited ... {Earth's heat sources 2012.ppt} {light scattering 2012.ppt} ... students only Answers (…
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{Earth's heat sources 2012.ppt}
{light scattering 2012.ppt}
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students only Answers (note - 6 Mb file on Google Drive, private to SHC)
I am moving in some material from the old L3 Science/Physics standard; some links have been lost. I will rebuild this as I have time.
To get the full material go to:
(view changes)
3:06 pm

### Monday, September 12

1. extremophiles edited ... Google Doc logbook: accessible to SHC students PDF logbook {logbook.pdf} {extreme environ…
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Google Doc logbook: accessible to SHC students
PDF logbook {logbook.pdf}
{extreme environment student booklet 2016.pdf}
(view changes)
5:49 pm
2. 5:48 pm

### Monday, July 4

1. Electricity edited ... Textbook examples Circuits3 Magnetism and electromagnetism {http://www.parentinghealthybabi…
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Textbook examples Circuits3
Magnetism and electromagnetism
We all know that magnets can pick up certain objects, such as pins or nails. These substances are termed ferromagnetic, and are attracted towards magnets;
Iron is the best known magnetic substance, but nickel, cobalt, various alloys and the oxide of iron known as ferrite or magnetite are all capable of being attracted to magnets or made into magnets.
The attractive force produced by a magnet is due to a magnetic force field we will discuss in more detail later.
{https://www.kjmagnetics.com/images/blog/water-compass400.jpg}
A long thin magnet is called a bar magnet. If you float a magnet on water, or allow it to rotate (e,g, by suspending it balanced on string), the magnet will slowly turn around until one end is pointing roughly north. This 'north seeking' end of the magnet is termed the north end of the magnet:
Experimenting with two bar magnets will quickly show you that the north end of one magnet repels the north end of another. The north and south end of two magnets attract each other, and two south ends will also repel. This can be summarised as
- like ends of a magnet repel
- unlike ends attract.
The magnetic force field around a bar magnet can be 'seen' if you sprinkle ironsand or iron filings on a piece of paper with a magnet underneath:

(notes in preparation, use text in the interim)
Review of this unit
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4:59 pm

### Monday, June 27

1. Electricity edited ... Cloze exercise for vocab {Electricity review cloze 1.pdf} {electricity crossword.pdf} Lif…
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Cloze exercise for vocab {Electricity review cloze 1.pdf}
{electricity crossword.pdf}
Lifting electromagnets question
(view changes)
4:56 pm