## ELECTRICITY from 2017

FINISHED!! 29/11/17

Electricity 2017  Final word version of the final electricity unit for Lockerbie

The booklet is large as it contains lots of questions for you to practice, some practicals for you to complete and some notes. These are currently in for copying, but hopefully in the next few days you should get your own copy. Please return it to the faculty on 8th May!

The section numbers are linked to the compendium with all the things to cover in National 5 Physics.

They are large notes so that you ought to be able to work your way through whether you are in class or away at college etc.

Electricity 2017 19 word version

Here are some additional notes that might help as you go through the materials. Check out the post on using your calculators to measure resistance (I’ll add the link here when I’ve found the post!)

Traces

EE1 – Electricity LOCKERBIE The old electricity notes (based on a colleagues work- thank you and I’ll find out who you are), these will be superceded when the document above is completed.

AC_DC[1] This is a powerpoint presentation that someone passed to be in the days of SG. It covers AC and DC traces

resistor network Try this when you think you have got to grips with resistances in series and parallel.

Elect & elect D&G Prob Book no answers These are some great little questions by Mr Belford from Dumfries Academy, but some of the numbers are a little bit fictional!

Elect & elect D&G Prob Book no answers The above document as a pdf file.

Voltage (2)

Voltage Analogy

VOLTAGE DIVIDER FORMULAE The formula sheet for voltage dividers

VOLTAGE divider circuits (2)

VOLTAGE divider circuits2

POTENTIAL DIVIDERS2

POTENTIAL DIVIDERS

VOLTAGE divider Q  Practice those horrible voltage divider questions with this pdf version of the document below. The answers are given for you to check. VOLTAGE divider Q

Ring main   Based on the SG course notes and not really in the N5 course, but it might give a little background to why when calculating the fuse rating for an appliance you use 240V and not the 230 V as stated.

…… to be continued!

## Voltage

Many teachers think that voltage is too difficult a concept for S1 students to understand. By the time students get to AH we expect them to be fully knowledgeable about voltage, but we don’t clearly explain it to them as we go along. I am as guilty as the next person of doing this so… . My new mission is to teach voltage as best and as fully as I can to S1 and build on the concept each year so that by AH they will feel confident about this work.

Having met Gill Arbuthnott at the Edinburgh International Book Festival (see post in Blog) I was really impressed with the way she tries to explain difficult concepts early on. She has given me permission to reproduce her page 16 on The Volt here.

The Volt

This was named after Alessandro Volta It is a unit of measurement in electricity. It tells us how much energy an electric charge has. You sometimes hear people saying things like, “The number of volts running through the circuit is…”. This doesn’t actually make sense! It’s like saying, “The height running through the mountain is 1000 metres.” Heights don’t run, and neither do volts. There is no Usain Volt!

What is a volt?

So what is a volt? Imagine you are in a building with stairs and a lift. You carry a tennis ball up one floor in the lift, and let it roll back to ground level down the stairs. A battery is like the lift – it’s a way of giving energy to something. In the building this is the ball – in electrical terms it’s an electron.

The ball rolling down the stairs is losing energy. In our circuit the equivalent is the electrons losing their energy to power a bulb. The voltage is equivalent to the height you take the ball up in the lift – more height is equivalent to greater voltage. And the distance the ball goes up in the lift must be the same as the distance it comes down by the stairs.

There are plenty of pictures in the book, but I didn’t think it was as easy to reproduce them. The book is full of more really interesting stuff, and even material about coins that Mr Chemistry opposite Mrs Physics didn’t know about (but then he’s far too young!)

http://www.bloomsbury.com/uk/a-beginners-guide-to-electricity-and-magnetism-9781472915740/

Definition: Potential difference is the amount of work done to move an electric charge from one point to another.

or

Definition: The definition of voltage is the electromotive force or the electrical potential difference between two points in a circuit expressed in volts.

Voltage is a scalar quantity. The SI unit of voltage is the volt, such that 1 volt = 1 joule/coulomb.

The easiest way to understand voltage is to use a water analogy. Using a hose as an example, think of voltage as the amount of pressure forcing water through a garden hose. The higher the pressure in the pipe the more water is forced through the pipe each second. The greater the voltage, the greater the flow of electrical current (that is, the quantity of charge carriers that pass a fixed point per unit of time Q=It) through a conducting or semiconducting medium for a given resistance to the flow.

One volt will drive one coulomb (6.24 × 10 18 ) charge carriers, electrons, through a resistance of one ohm in one second.

Voltage can be direct or alternating. A direct voltage maintains the same polarity at all times. So charges always flow in one direction. In an alternating voltage, the polarity reverses direction periodically. The number of complete cycles per second is the frequency, which is measured in hertz (one cycle per second). An example of direct voltage is the potential difference between the terminals of a cell. Alternating voltage exists between the mains positive and negative.