Physics end Flashcards
Define and give units for:
electrostatic force Electric potential differenceElectronvolt
The force between two charged bodies.is the work done per unit charge on a small positive test charge moved between the points; volts = one joule per coulomb. also called voltagedescribes the energy carried by a particle. The work done when an electron moves through a potential difference of 1 volt; eV
Describe:Hollow conductors:Pear shaped conductor:Corona Discharge:
hollow charged objects, within the hollow part there is a zero charge. Concentrated charge density on point because of the difference in size.The strong electric fields, near a point of a pear shape, may be large enough to ionise the molecules in the air in the vicinity of the sharp points. This results in a charge movement away from the conductor
Define and give units for:Electric field strength
The electric force per unit charge (q) experienced by a small positive test charge when placed at that point in the field; Newtons per Coulomb or Volts per meter
State:my boi Coulomb’s law
The electric force of attraction or repulsion between two charged objects is directly proportional to the products of the two charges and inversely proportional to the square of the distance between their centres.The electric force acts along the line joining the centres of the charges as though the charge were concentrated at a point.
Describe and show units for:Electric current:
The flow of positive charge, opposite to the flow of electrons.Measured in the Ampere, or a flow of one coulomb per second.
Derive:E=F/q
From coulombs law:F = 1/(4pieo) x (q1q2)/(r^2)E= 1/(4pieo) x q/(r^2)r^2=1/(4pieo) x (q1q2)/FTherefore:E= 1/(4pieo) x q/1/(4pieo) x (q1q2)/FCancels probably to get:E=F/q
Derive:E=V/d
Since V=W/q therefore W=VqAnd W=fdAnd F=EqVq=fdVq=EqdV=EdE=V/d
Explain:The electric forces are consistent with newtons laws
The magnitude of force acting upon two charges due to their electric fields is the same. Newtons third law states that for every action there is an equal and opposite reaction. Electric forces are consistent with newtons third law.
Describe:The motion of charged particles parallel or antiparticle to a uniform electric fieldComparing the motion of a projectile to motion of a charged particle in a uniform electric field.
similar to gravitational acceleration, instead of acceleration due to gravity, there is acceleration due to electric field.
You doing a graph, what you do.What are the units for the lineWhat are the axis
HEADINGY OVER XX IS THE INDEPENDANT
Convert energy from electonvolts to joules.Convert energy from joules to electonvolts.Apply the equivalent of W=q♤V
Multiply electronvolts 1.6x10^-19 the charge of an electron.Divide joules by 1.6x10^-19 the charge of an electron.W = q♤V = 1.6x10^-19 x 1 = 1.6x10^-19 joules
Define and give units for:Magnetic field.Visual appearance of magnetic fields.
The region surrounding a magnetic material or a charge in motion. Such as a current carrying-conductor.This is a vector quantity, appearing as concentric circles around the conductor. The number of field lines indicate the strength of the field at a point.The unit is the Tesla (T) with the symbol B
Describe the right hand rule:
The thumb points in the direction of conventional current ant the curl of the fingers indicate the direction of the magnetic field produced.
Describe:Visual representation of current with “x”Visual representation of current with “o”
The x refers to a current of magnetic field traveling into the page, and the dot refers to the current or magnetic field travelling out of the page.
Describe:SolenoidsFactors affecting strength of magnetic field::
Many coils of wire. Acts like a bar magnet, having a north and south pole.This is also referred to an electromagnet. The magnetic field inside the loops are stronger than outside.Factors that may change the magnetic field strength are:The number of coilsThe magnitude of current traveling throughPresence of an iron or conductive core
Express: magnetic field strength, in relation to gravitational and electric field strength-
Magnitude is directly proportional to the current. As gravitational field strength is proportional to the massElectric field is directly proportional to charge. Magnetic field strength is inversely proportional to the radial distance from the conductor. Gravitational field strength is inversely proportional to the distance from a mass.Electric field strength is inversely proportional to the distance from a charge.B=F/il
describe and illustrate:Motion of magnets in magnetic fields-
Anything that produces a magnetic field will experience a force within a magnetic field, like a compass which is essentially a small magnet.
Express-Force on a straight current carrying conductor is Proportional to:And On a charged particle
Current flowing through the conductorLength of conductorMagnetic field strengthSin/Cos of angle to magnetic fieldOn a charged particle, it is dependant on the magnitude and direction of the velocity.
Describe-Direction of the force on a current-carrying conductor and individual charges:
Using the right palm rule The thumb points in the direction of conventional current and the fingers point in the direction of magnetic field. The force acts perpendicularly away from the palm of the hand. A positive charge will travel like this, a negative charge will travel in the opposite direction.The force on a current element that is parallel or antiparallel to a magnetic field is zero.
Describe-Motion of charged particle in uniform magnetic field:
Since a charged particle, moving at right angles to a uniform magnetic field, experiences a force of constant magnitude at right angles to the velocity. The charge changes direction without a change in speed. The magnetic force provides the centripetal acceleration required for uniform circular motion.
Derive-Radius of the circular path of a charged particle moving at right angles to a uniform magnetic field of magnitude B.
F(centripetal)=F(magnetic)(MV^2)/r=qvBr=MV/qB
Describe-Cyclotron components:
An electromagnet is positioned above and below two D-shaped hollow conductors, Producing a uniform magnetic field inside the dees.
Derive and explain meaning of-Period of circular motion of an ion in a cyclotron:
T=(2piR)/vBut r=(mv)/qBT=(2pim)/qBThe period does not depend on speed of the ions. Meaning the period of all ions in cyclotron are the same, meaning they reach the gap at the same time interval, regardless of the speed, thus the potential difference can be reversed on a regular basis.
Derive and explain meaning of-Kinetic energy of ions emerging from cyclotron:
Ek=(Mv^2)1/2 But r=mv/qB, so v=(rqB)/mK=(M(rqB/m)^2)½K=(rqB)^2/(2m)The kinetic energy is independent of the potential difference across the dees. A larger potential difference does not mean more kinetic energy to the ions, it means the ions will cross the electric field fewer times before they emerge from the cyclotron.
Describe and express with units:magnetic flux-
Is a measure of the number magnetic field lines passing through an area. Being the product of magnetic field strength B and the area A. Flux=BAcos(theta)Where theta is the angles between the area and a line normal to the magnetic field.The units for magnetic flux is the Weber (Wb)
ExpressUnits of area conversion, mm, cm, m, km
cm^2 -> x10^-4 -> m^2mm^2-> x10^ -6 -> m^2mm^2 -> x10^-2 -> cm^2km^2 -> x10^-6 -> m^2
DescribeElectromagnetic induction:
A changing magnetic flux induces a potential difference in a conductor.This induced emf (electromotive force) causes a current to flow. Electrons in the conductor are forced to move given by F=qvB sin(theta). This causes one end of the conductor to become more negative or positive.
Describe and ExpressFaraday’s law:
The induced emf is equal to the rate of change of the magnetic flux.e=Change in flux / change in timeThe SI unit of emf is the volt (V)This may be continued to a situation where there are several loops, giving the equation:emf=(n) Change in flux / change in time.
Express:Emf for a changing area or magnetic field:
For a changing areaemf= (n) (B) (A2-A1)/ change in timeFor a changing magnitude of magnetic field strength.emf=(n) (A) (B2-B1)/ Change in time
Describe:Lenz’s lawapplication of lenz’s law to solenoid
Lenz’s Law states that the induced emf creates a current in a direction that opposes the change in magnetic flux. This may occur through the motion of a magnet and a solenoid, causing the poles to reverse depending on the motion of a magnet, to repel or attract the magnet in motion.
Describe:Lenz’s law in terms of the conservation of energy
If the induced poles of the solenoid were to be opposite, then, the magnetic force of attraction between the two unlike poles would cause the magnet to accelerate towards the solenoid. Inducing a greater current in the solenoid, the magnet would further accelerate. This would continue to speed up, increasing the kinetic energy. The energy created would violate the law of conservation of energy. The induced current must therefore flow in a direction to oppose the change in magnetic flux.
Describe:Eddy current:
Is the current induced in little swirls on a large solid conductor due to a changing magnetic field. These occur in accordance with Lenz’s law so that they have a direction that will flow to oppose the change in magnetic flux.
Describe:Generators:
A generator uses a fixed magnet to generate emfs in rotating conducting loops for electricity production. A generator therefore converts rotational mechanical energy into electrical energy.
Describe:Lamentation:
To avoid large eddy currents being produced in a solid conductor, slits can be cut into the metal.
Describe and explain:Transformers:
Allow generated voltages to be either increased or decreased before they are used. This is done through primary and secondary coils, each coil with it’s own number of loops. Given the relationship:VpNs=VsNpThese are wrapped around an iron core to increase the strength of the magnetic field. Since the same magnetic flux is passing through both coils, the emf for both are the same. Given that the number of loops vary, then the potential difference will change, changing the volts.Though energy is conserved, so it is transferred from current.
Describe:Step-up and step-down transformers.
A step up transformer.When the number of coils in the secondary coil is greater than the primary. Resulting in a greater potential difference in the secondary coil, increasing voltage. The output current is lower than the input currentA step down transformer.When the number of coils in the secondary coil is lesser than the primary. Resulting in a lesser potential difference in the secondary coil, decreasing voltage. The output current is greater than the input current.
ExplainWhy cyclotrons are positioned near the place where they need to be used?What if they were not in the same place?
Used to create medical isotopes or in the industry.Isotopes have short half lives, thus they need to be kept in the hospital where they will be used, so that the isotopes do not decay before used. If there was not a readily available cyclotron, then the isotope would have to be made elsewhere and transported. The time would require more of the isotope to be made to compensate for the radioactive decay.Having cyclotron on site reduces costs and increases the number of scans available to patients in time. Some isotopes have short half lives, making them impractical to ship
Describe:Components of generators:
Magnets: Produce a uniform magnetic fieldIron core: A soft iron that serves to maximise the magnetic field. It is usually laminated to reduce effect of eddy currents which are bad.Rotator coils: Loops of wire around the iron core. A current is induced in the rotor coils as they rotate in the magnetic field.Split ring communicator: 2 metal half rings connect either end of coils to brushes. Brushes: 2 blocks on either side of communicator. Provide electrical contact to an external circuit.Axle: A rod passing through iron core and coils to provide an axis or rotation for the rotator coils.AC: Induced current is not reversed every half rotation of the coils.DC: Induced current is reversed every half rotation of the coils.
Describe:Why the high voltage is used in transmission lines from generator to consumer.
This is to keep the current low, as some energy is lost to the surroundings as heat due to resistance. To minimise the energy loss, the current is kept low by using a high transmission voltage.
you’re given a she question, what you do?
Identify the key pointsExplain the points relation to physicsImpact on society
Describe:function of cyclotron
Charged particles are accelerated by a uniform electric field in the. The electric field does work on the ions and transfers kinetic energy to the ions (W=qV=Ek=(mV^2)/2).The uniform magnetic field causes the charged particles to move in a circular path so that they return to the electric field by providing centripetal acceleration. The current passing through each dee, alternates, reversing the electric field before the particle returns, accelerating it further.
Explain:transmission of radio or television waves.
Conductors convert electric current into EM radiation and vice versa by alternating current, causing oscillating electrons which oscillate an electric field, producing oscillating magnetic field perpendicular. Frequency of continually reproducing waves equals that of oscillation of electrons.
Explain:Reception of radio or television waves.
Electrons in receiving antenna is forced to oscillate by electric field of radio wave, they will oscillate in same frequency as electric field. Producing alternating potential difference in receiver.Force (F=Eq)
Describe:orientation of the receiving antenna
Must be in same plane of polarisation of radio or television waves, or parallel to the producing antenna.
Describe:Electromagnetic waves
are transverse waves made up of mutually perpendicular, oscillating electric and magnetic fields which continually reproduce from eachother.
