M & G syllabus (2 Viewers)

[MuffinMan]

Heres section 1 of the syllabus


* discuss the effect on the magnitude of the force on a current-carrying conductor of variations in:
– the strength of the magnetic field in which it is located
– the magnitude of the current in the conductor
– the length of the conductor in the external magnetic field
– the angle between the direction of the external magnetic field and the direction of the length of the conductor

Factors affecting the magnitude of the force depends on the following factors:
- The strength of the external magnetic field. The force is proportional to the magnetic field strength, B.
- The magnitude of the current in the conductor. The force is proportional to the current, I
- The length of the conductor in the field. The force is proportional to the length, l
The angle between the conductor and the external magnetic field.
The force is at maximum when the conductor is at right angles to the field, and is zero when the conductor is parallel to the field.

The magnitude of the force is proportional to the component of the field and the conductor. If θ is the angle between the field and the conductor, then the force is the maximum value multiplied by the sine of θ.

This can be expressed mathematically as:
BIl sin θ

[Ref: p100, Jacaranda HSC Physics, 2nd ed.]

*describe qualitatively and quantitatively the force between long parallel current-carrying conductors:

f a finite distance separates two parallel current-carrying conductors, then each conductor will experience a force due to the interaction of the magnetic fields that exists around each. The magnetic field strength at a distance, d, from a long straight conductor can be found using the formula

B = (kI)/d

Where k = 2.0 x 10-7 N A-2

The magnitude of the force experienced by the length, l, of a conductor due to the external magnetic field provided by another conductor is

F = I2l(kI₁ / d)

[Ref: p101-103, Jacaranda HSC Physics, 2nd ed.]

define torque as the turning moment of a force using:
τ= Fd

A torque can be thought of as a turning effect of a force acting on an object. It is easier to rotate an object if the force, F, is applied at greater distance, d, for the pivot axis to its point of application. It is also easier to rotate an object if the force is at right angles to a line joining the pivot axis to the point of application.
The torque, τ, increases when the force, F, is applied at a greater distance, d, from the pivot axis. It is greater when the force is applied at right angles to the line joining the point of application of the force and the pivot axis. The SI unit for torque is the newton metre (N m), and is found using the equation:

τ = Fd sin θ

[Ref: p101-102, Jacaranda HSC Physics, 2nd ed.]

identify that the motor effect is due to the force acting on a current-carrying conductor in a magnetic field

A current carrying conductor produces a magnetic field. When the current-carrying conductor passes through an external magnetic field, the magnetic field of a conductor interacts with the external magnetic field and the conductor experiences a force. This effect was discovered by Michael Faraday (1791-1867) and is known as the motor effect.

The direction of the force on a current-carrying conductor in an external magnetic field can be determined using the right-hand push rule

*describe the forces experienced by a current-carrying loop in a magnetic field and describe the net result of the forces

The forces experienced by a current-carrying loop in a magnetic field depend on the orientation of the loop relative to the magnetic field. You will need to describe both the direction and the relative magnitude of particular forces, in addition to the net result of all forces.

Assume, for simplicity of discussion, that the axis of a rectangular coil is perpendicular to the magnetic field, and that the long sides of the coil are parallel to the axis and equidistant from it.
• Each long side of the coil experiences a force whose magnitude does not change throughout a rotation of the coil, since the sides always remain perpendicular to the field. The force on each long side can be shown, by the right-hand palm rule, to be always in the same direction throughout a rotation of the coil, opposite in direction to the force on the other long side, and always perpendicular to the axis.
• Each end of the coil will experience a force which varies from zero, when the plane of the coil is parallel to the field, to a maximum when the plane of the coil is perpendicular to the field. The forces on the two ends can be shown, by the right-hand palm rule, to be opposite in direction, always parallel to the axis, and alternating in direction through a full rotation of the coil.
• The force on each long side produces a torque about the axis. As the forces are in opposite directions, and their lines of action are on opposite sides of the axis, they produce a torque in the same direction. Thus, their effect is to rotate the coil about its axis. The net torque is at its maximum when the plane of the coil is parallel to the field, as the perpendicular distance, d, to the line of action is maximum, and reduces to zero as the plane of the coil rotates to be perpendicular to the field, as the line of action of each force is then through the axis (d = zero). The direction of the torque alternates through a complete rotation of the coil: its direction is always to rotate the coil to be perpendicular to the field.
• As the forces on the two ends are always opposite in direction, and always parallel to the axis, their net effect is zero.
• For any current-carrying loop in a magnetic field, free to rotate about any axis, the net effect of the forces will be such as to rotate the loop to lie perpendicular to the magnetic field. A current-carrying loop orientated in a plane at right angles to a magnetic field will experience no net force.

*describe the main features of a DC electric motor and the role of each feature

see attatchment

identify that the required magnetic fields in DC motors can be produced either by current carrying coils or permanent magnets

The magnetic field of a DC motor can be provided by permanent magnets, or by electromagnets. The permanent magnets are fixed to the body of the motor. Electromagnets can be created using a soft iron shape that has coils of wire around it. The current that flows through the armature coil can be used in the electromagnetic coils.

 

[richz]

nice work hsc

 

[Rickdog]

grand.
thanks

 

[MuffinMan]

second section here
i couldnt be bothered with the formatting of bos so yeah sorry

*outline Michael Faraday’s discovery of the generation of an electric current by a moving magnet

• In August 1831, Faraday discovered electromagnetic induction. This is the generation of an emf and/or electric current through the use of a magnetic field.
• Faraday attached two wires through a sliding contact to touch a rotating copper disc located between the poles of a horseshoe magnet. This was the same as moving a magnetic field near an electric circuit. This induced a continuous direct current. Faraday had invented the first electric generator. Prior to this, continuous electricity could only be produced by batteries or galvanic cells.
• Faraday's explanation was that the electric current was induced in the moving disc as it cut a number of lines of magnetic force emanating from the magnet (the magnetic field). The wires allowed the current to flow in an external circuit where it could be detected.
*define magnetic field strength B as magnetic flux density
*describe the concept of magnetic flux in terms of magnetic flux density and surface area

The magnetic field in a region can be represented diagrammatically using field or flux lines. Magnetic flux is the name given to the amount of magnetic field passing through a given area. It is given the symbol ΦB. In the SI system, ΦB is measured in Weber (Wb). If a particular area, A, is perpendicular to an uniform magnetic field of strength, B then the magnetic flux ΦB is the product between B and A.

ΦB = BA

The strength of magnetic field, B, is also known as the magnetic flux density. It is the amount of flux passing through an unit area. In the SI system, ΦB is measured in tesla (T) or weber per metre (Wb m-2)

The magnetic flux, ΦB passing through an area is reduced if the magnetic field is not perpendicular to the area, and ΦB is zero if the magnetic field is parallel to the area. The above relationship can be written as:

ΦB = B|A

Where B| is the component of the magnetic flux density that is perpendicular to the area, A

[Ref122-123, Jacaranda HSC Physics, 2nd ed.]

*describe generated potential difference as the rate of change of magnetic flux through a circuit

For a current to flow through a galvanometer, there must be an electromotive force (emf). The magnitude of the current through the galvanometer depends on the resistance of the circuit and the magnitude of the emf generated in the circuit.
Faraday noted that there had to be change occurring in the apparatus for an emf to be created. The quantity that was changing in each case was the amount of magnetic flux threading (or passing through) the coil in the galvanometer circuit. The rate at which the magnetic flux changes determines the magnitude of the generated emf.
This gives Faraday’s Law of Induction which can be stated as follows

The induced emf in a circuit is equal in magnitude to the rate at which the magnetic flux through the circuit is changing with time.

ε = (ΔΦB)/ (Δt)

The negative sign in the above equation indicates the direction of the induced emf.

When calculating quantities using Faraday’s Law of Induction

ΔΦB = ΦBfinal – ΦBinitial

[Ref: p123, Jacaranda HSC Physics, 2nd ed.]

*account for Lenz’s Law in terms of conservation of energy and relate it to the production of back emf in motors

Lenz discovered a way to predict the direction of induced current . Lenz’s Law can be stated as follows:
An induced emf always gives rise to a current that creates a magnetic field that opposes the original change in flux through a circuit.

This is a consequence of the Principle of Conservation of energy. The minus sign in Faraday’s law of induction is placed to remind us the direction of the induced emf.

The Principle of Conservation of Energy states:
Energy cannot be created nor destroyed, but it can be transformed from one form to another.

To create electrical energy in a coil, work must be done. Energy is required to move a magnet towards or away from a coil. Some of this energy is transformed into electrical energy in the coil.

[Ref: p124-125, Jacaranda HSC Physics, 2nd ed.]

*explain the production of eddy currents in terms of Lenz’s Law

Electric motors use an input voltage to produce a current in a coil to make the coil rotate in an external magnetic field. Emf is induced in a coil that is constantly rotating in an external magnetic field because the amount of magnetic flux that is threading the coil us constantly changing as the coil rotates. The emf induced in the motors coil as it rotates in an external magnetic field, is in the opposite direction of the input voltage, or supply emf.

 

[MuffinMan]

* Describe the main components of a generator

The stationary functionary parts of a generator are called the stator, whereas the rotating parts are called the rotor. Generators consist of the following:
- an armature
- a field structure or magnetic field (this can be in the form of a permanent magnet or an electromagnet)
- slip rings and brushes (to take the induced current away)
- a commutator (DC generators only)

* Compare the function and structure of a generator to an electric motor

Parts of a motor

Armature – rotates to transfer electrical energy to kinetic energy
Magnets – provides field for interactions with field induced by supply current to produce torque
Coils – carries the supply current
Commutator – changes direction of supply current every half rotation so torque is produced in a constant direction.
Brushes – provide electrical connections to supply the current to the coil

Parts of a generator

Armature – rotates to transfer supply kinetic energy to electrical energy
Magnets – provide field to induce current into the rotating coil
Coil – movement of coil in magnetic field induces current
Commutator (DC only) – changes direction of output current every half rotation so DC results
Brushes – provide electrical connections for output current

 

[currysauce]

* Describe the main components of a generator

The stationary functionary parts of a generator are called the stator, whereas the rotating parts are called the rotor. Generators consist of the following:
- an armature
- a field structure or magnetic field (this can be in the form of a permanent magnet or an electromagnet)
- slip rings and brushes (to take the induced current away)
- a commutator (DC generators only)

* Compare the function and structure of a generator to an electric motor

Parts of a motor

Armature – rotates to transfer electrical energy to kinetic energy
Magnets – provides field for interactions with field induced by supply current to produce torque
Coils – carries the supply current
Commutator – changes direction of supply current every half rotation so torque is produced in a constant direction.
Brushes – provide electrical connections to supply the current to the coil

Parts of a generator

Armature – rotates to transfer supply kinetic energy to electrical energy
Magnets – provide field to induce current into the rotating coil
Coil – movement of coil in magnetic field induces current
Commutator (DC only) – changes direction of output current every half rotation so DC results
Brushes – provide electrical connections for output current

great work, but all u have done is talk about structure, what about comparison of function?

 

[MuffinMan]

* describe the differences between AC and DC generators

The effective difference between DC and AC generators is the contact between the coil and the external circuit. DC Generators have a split ring commutator whereas an AC generator has two slip rings or continuous ring contact with the brushes

* discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer

The resistance of a metallic conductor is proportional to its resistivity and is inversely proportional to its cross sectional area. Thus there are difficulties involved in transmitting electrical energy at low voltages over large distances. The solution is to use step up transformers to step up voltages before transmission. If the voltage is increased, the current is reduced. The power loss of transmission lines is given by the formula:

P_loss = I²r

If the transmission voltage is doubled, the current is halved and the power loss is reduced by a factor of four. If the current is reduced by a factor of 10, the power loss is reduced by a factor of 100. This has lead to a significant impact on society. If transformers were not used in power distribution system, either power stations would have to be built in the cities or towns. This means that fossil fuel stations would dump their pollution on the near-by population centres. Otherwise users of electricity have to be located near the power stations. This would have meant that industries and population centres would have to be located near the energy sources.

* assess the effects of the development of AC generators on society and the environment

The development of electrical generators and motors has affected many phases of modern life, but not always in the ways predicted. It was first predicted that electric machines would do all the physical labour, backbreaking housework would be eliminated by electrical gadgets so that people would have much more leisure time. However, instead of this, it has caused a reduction of unskilled jobs and an increase in unemployment.
Another prediction is that the population would become more decentralised. This prediction arose during the 19^th century when people were drawn into big cities where the power supplies were located. However, the development of transformers and the power distribution system meant that cities, factories and other industries could be located large distances from power stations. Thus many moved out to the outer suburbs and thus the opposite of decentralisation occurred.
The use of electrical energy and motors has also a dramatic effect on the environment. Fossil fuel power stations have environmental effects such as thermal pollution, acid rain and air pollution due to the release of particles and oxides of nitrogen and sulfur. The huge amounts of carbon dioxide released by power stations contribute to the enhanced greenhouse effect.

* describe the purpose of transformers in electrical circuits

Transformers are devices that increase or decrease AC voltages in electrical circuits. They are used in television sets to apply the very high voltages required to drive cathode ray tubes. They are also used in electronic appliances such as radios to provide lower voltages for amplifier circuits.

* compare step-up and step-down transformers

If the voltage out is greater than the voltage in it’s a step up transformer. (The number of turns in the secondary coil is greater than the number of turns in the primary coil).
If the voltage out is less than the voltage in the device is called a step down transformer. (The number of turns in the secondary coil is less than the number of coils in the primary coil).



* identify the relationship between the ratio of the number of turns in the primary and secondary coils and the ratio of primary to secondary voltage

An alternating voltage, V_p is applied to the primary coil, producing an alternating magnetic field in the iron ring so that it passes through the secondary coil as well. As the magnetic flux through the secondary coil is continually reversing direction, an induced alternating voltage V_s is produced across the ends of the secondary coil. At the same time an induced voltage (back emf) is produced across the ends of the primary coil and is connected to the secondary coil (no current flows), no energy is lost in the secondary circuit. Thus no energy is dissipated in the primary circuit so that the back emf is equal to the applied voltage. Thus the current induced in the primary and secondary coils are in the same ratio as the number of turns in the coils.

V_p / V_s = N_p / N_s

* explain why voltage transformations are related to conservation of energy

The Principle of Conservation of Energy states that energy cannot be created nor destroyed but it can be transformed from one form to another. This means that if a step up transformer gives a greater voltage at the output, there must be some kind of trade-off. The rate of supply of energy to the primary coil must be greater than or equal to the supply energy from the secondary coil. There is a decrease in useable energy wherever energy is transformed. The ‘lost’ energy is said to be ‘dissipated’, usually as thermal energy.
The rate of energy is known as ‘power’ and is given by the equation:
P = VI

* explain the role of transformers in electricity sub-stations

As electricity transmitted at high voltages and low currents suffers less energy loss than that transmitted at lower voltages and high current. Transformers are used in electricity distribution systems, to increase the voltages generated at a power station for distribution across the country, and then in electrical substations, to decrease the voltage to a level where it can be used in electrical appliances.

*discuss why some electrical appliances in the home that are connected to the mains domestic power supply use a transformer

Some appliances run on potential differences less than 240V and are supplied by a small transformer unit which plugs into the 240V AC wall socket. A transformer can also be used to isolate a device from the dangerous domestic supply as the supply circuit is not physically connected to the device as it may be through an extension cord.

* discuss the impact of the development of transformers on society




* describe the main features of an AC electric motor

An AC generator can be run as an AC motor if it is first of all rotated at the same frequency (50Hz) as the alternating voltage which is supplied through the slip rings. Instead of the split-ring commutator reversing the voltage every half-cycle, the applied voltage itself reverses. Because their speed is accurately controlled by the frequency of the voltage supply such motors are used in clocks. However, without assistance they are not self-starting because they cannot run at frequencies other than that of the supply.

When a metal wheel is rotated between the poles of a horseshoe magnet eddy currents are induced in it in such a direction that a force acts to slow the wheel down, that is to reduce the relative velocity between the magnetic field and the wheel. Thus effect can be used to rotate the wheel by moving the magnet around the rim of the wheel. In this case the magnetic field moves, eddy currents are induced in the metal in such a direction that the wheel begins to follow the field as to reduce the relative velocity between them.

In an induction motor two at the least of fixed electromagnets (the stator) are positioned around the rim of the metal wheel (the rotor) and an alternating current is supplied to each so that the magnetic field reaches its maximum slightly after the one before. A rotating magnetic field will be created and the wheel will move in the direction the field moves in order to reduce the relative velocity between the wheel and the field. One of the advantages of such a motor is that there is no direct contact between the rotor and the stator.

edit: can someone help me fill out the dp im missing?
thanks

 

[Jago]

i would, but all my notes are handwritten.

sorry.

 

[MuffinMan]

the missing dp

The development of transformers made it possible to transmit electrical energy efficiently over great distances. This has had a range of impacts on society.
Even very remote communities now have access to grid-supplied high-voltage electricity which is stepped down locally by transformers. This has raised living standards in rural communities through provision of, for instance, electric lighting, refrigeration and air conditioning, and increased the scope of rural industries.
Large cities have been allowed to spread, because electricity is readily available as an energy source, thanks to transformers. This has led to social dislocation in urban “deserts”, as people have moved further from family and friends and workplaces.
Industry is no longer clustered around power stations or other sources of energy. Power stations can be in remote locations and high-voltage electrical energy can be distributed almost anywhere, to be stepped down near the point of use. This has allowed industries to be decentralised and has facilitated the development of industrial areas away from residential areas. This has relocated pollution away from homes, but it means that many people now spend significant time travelling between home and work.
With the development of the transformer, people have changed the way they live, as electricity to every home has become an affordable necessity rather than a luxury.

 

[treelovinhippie]

Nice, have you put this in the resources section?

 

[MuffinMan]

Nice, have you put this in the resources section?

no last time i tried to put something in the resources section it never came up...so i give up

 

[Jago]

From what i can see, most of these solutions can be found in the Jacaranda book.

but nonetheless, <3 for typing it in syllabus format

 

[MuffinMan]

no worries matey i think i got a few more too

 

[holla back girl]

wow, you write notes for phys?
you must be kicking ass in yours school

 

[Jago]

the new physics syllabus promotes regurgitation. what can we do...

 

[holla back girl]

btw...yeh i agree...mostly memory....which is why teh girls are kicking ass in phys...is that the same in your school

 

[Jago]

Nope. Don't get me wrong, some of the girls do extremely well in physics, but some of the guys in the course....they KNOW their stuff.

 

[physician]

btw...yeh i agree...mostly memory....which is why teh girls are kicking ass in phys...is that the same in your school

well the top of my physics class is a girl with an everage of 95%.. she's the only girl out of a class of 4...

but i think its a combination of ability to memorise along with hard work,dedication and the general positive attitude towards her studies... but i mean in most cases u need to understand the stuff to memorise it in the first place.. so i'd say a combination of all these factors get's u top marks... (duh!!!.. lol)

 

[holla back girl]

but i mean in most cases u need to understand the stuff to memorise it in the first place.. so i'd say a combination of all these factors get's u top marks... (duh!!!.. lol)

i don't appreciate the duh..but yeh...i agree with you there.
Well at my school...i would have to say the top 10 in phys are all girls. But the new physics syllabus certainly has less calculations and more written+memory.
i mean...i think i do more calculations in chemistry tests than physics tests.

 

[physician]

i don't appreciate the duh..but yeh...i agree with you there.
Well at my school...i would have to say the top 10 in phys are all girls. But the new physics syllabus certainly has less calculations and more written+memory.
i mean...i think i do more calculations in chemistry tests than physics tests.

I apologies ... I din't really mean to offend anyone if that's how u took it... sorry!!!

yeh I totally agree with u on that part...

going over my phyiscs half yearly the other day.. I realsied i used up 10 pages of working paper and out of the 10, 7 where filled with solid writing... hardly any calculations.. and besides the calculations aren't all that challenging anymore.. at least not from what i've seen.. but then again i've only gone through the 2001 HSC exam