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Physics Unit 4
Fichas del conjunto (74)
- 1kinetic energy (momentum)E=p²/2m
- 2Coulomb's Law for a point chargeF=kQq/r²
- 3Electric field strengthE=V/d
E=F/Q
the force per unit charge acting on a small positive charge - 4time constant (tau) for an RC circuit#the time it takes for the charge on a capacitor to fall to 1/e of its initial value when a capacitor is discharging
#the time it takes for the charge on a capacitor to rise to 1– 1/e of its final value when the capacitor is charging
τ = RC . τ is measured in s. - 5Quantity of Fluxthe number of magnetic lines of flux that pass through a certain point on a surface.It indicates the strength of the effect of the field.
∅=Bsinθ*A,
Where B is magnetic flux density - 6Magnetic flux linkageFlux Linkage = N∅
The amount of magnetic flux interacting with a coil of wire is known as the magnetic flux linkage
or
Flux Linkage=BAN - 7Faraday's law of electromagnetic induction states thatThe magnitude of an induced emf is proportional to the rate of change of magnetic flux linkage
- 8Lenz's LawThe direction of the induced e.m.f. or current is always such as to oppose the change producing it.
- 9What factors affect an induced current?Magnetic flux density of the field the wire is in; the speed of the relative motion of the wire to the field; the number of pieces of wire
- 10What is the Rutherford Geiger Mardsen experiment and explain their observationsMost of the alpha particles were undeflected because the atom is mostly empty space, most alpha particles did not get near enough to any matter to be affected
A few alpha particles were deflected by small angles because the charge is concentrated around NUCLEUS most alpha particles did not get near enough to a sufficiently large charge to be affected (draw diagram)
A very small proportion of alpha particles were deflected through large, obtuse angles, the NUCLEUS must be massive in order to cause this deflection because the mass of the atom is concentrated a very small space relative to the size of the atom
(draw diagram)
- 11thermionic emissionthe release of electrons from a heated filament
- 12Lorentz forcethe combination of electric and magnetic force on a point charge due to electromagnetic fields
- 13How do particle accelerators use electric and magnetic fields?electric fields speed up and increase the energy of a beam of particles; magnetic fields steer and focus the particles
- 14Why do particle accelerators require high energies to break particles into their constituents?a lot of energy is needed to overcome the binding energy within the particles
- 15baryonAny hadron made with a combination of three quarks
- 16mesonA hadron consisting of a quark and an anti-quark
- 17The symmetry of the standard quark-lepton model predicted...the top and bottom quarks
- 18Why can't induced current be directly used to charge a battery?Induced current is alternating
- 19How does rotating a coil of wire in a magnetic field produce a current?As the coil turns, there is a change in its magnetic flux linkage. This change produces an emf acting against the rotation which produces a current as the coil is a closed circuit
- 20What happens as a capacitor becomes fully charged?Electrons use the circuit connected to a capacitor to gather on one plate. Once the capacitor is fully charged, each plate has an equal and opposite charge
- 21How can a magnetic field deflect an ion into a circular path?The magnetic field acts perpendicular to the velocity of the ion. This generates a perpendicular force to the velocity of the ion, acting as the centripetal force for circular motion
- 22Conservation of MomentumProviding no external/unbalanced/resultant force acts total momentum before (a collision) = the total momentum after (a collision) Or the momentum of a system remains constant
- 23Uniform FieldA space or region where a force acts on a charged particle. The field strength is constant at all points.
- 24Fundamental particleCannot be split further/has no internal structure / not made up of other particles
- 25Relativistic(The particles are moving) close to the speed of light
- 26Role of magnetic field in particle accelerator/chamberTo produce a force at right angles to motion/a centripetal force to produce circular motion and enable the investigation of charge/mass
- 27Role of E field in particle accelerator/chamberTo provide force on the charged particle to give energy to / accelerate the particle
- 28Reason for linac tubes to get longerto keep the time spent in each tube the same
Or
so that frequency of alternating pd/voltage constant (do not accept reference to ac currents) - 29Difference between elastic and inelastic collisionsIn elastic collisions no kinetic energy is lost (almost impossible). In inelastic collisions some kinetic energy is lost deforming the colliding objects.
In both momentum before = momentum after - 30Describe an experiment to verify to principle of conservation of momentumMeasure the mass of each glider using sensitive top-pan balance
Measure the length of the card
Note the time (for the card) to pass the first(only m1) and second(m1+m2) light gate
Calculate the initial and final velocity using length (of card)/time, repeat to find error
Recognize the need to show that m1v1 = (m1+m2)v
Make sure the air-track is horizontal using spirit level
- 31Equation for linear acceleration of circular motionr * ω² = a
radius * angular velocity²
F= ma
subsitute a = r * ω²
F= mω²r - 32Equation to calculate energy stored within a capacitorE = 1/2*Q*V
E = 1/2*C*V²
E = Q²/2C
Q= charge
V= voltage
C= Capacitance - 33How to linearise dataN = N₀e^(-xt)
log both sides
ln N = ln (N₀e^(-xt))
ln N = ln N₀ -xt
very familiar to y =mx +c
Plot ln N to t and you should have a straight line with the y intercept of ln N₀
time constant is -1/gradient
(-)x = m - 34How to convert MeV/c² to Kgx10⁶x1.6x10⁻¹⁹ / (3x10²)²
- 35Name what is conserved in particle physicsMomentum, Mass-Energy, Charge, Bayron number, Lepton number, Strangeness (not in weak interactions)
- 36Beta plus decaypositron and electron neutrino
- 37Beta minus decayelectron and anti-electron neutrino
- 38How to get the cyclotron frequencyf = 1/T
T = s/v
T = 2πr / v
f= v/2πr
r = p/bq
f= vbq / 2πm
f= Bq / 2πm - 39How to get r= p/Bqmv²/r = Bqv
r = mv² / Bqv
r = mv/Bq
r= p/Bq - 40What are the 4 fundamental forces and their exchange particles
- 41Transformer equationPrimary voltage / secondary voltage = number of primary coils / number of secondary coils.
Power in = power out - 42Energy lost in an transformerEnergy dissapation to heat in coils:
P = I²R (joule heating)
Energy lost overcoming "internal friction" whilst magnetising and demagnetising the soft iron core (hysterisis)
Changing flux in soft iron core induces eddy currents. This causes heating effects and reduces efficiency. (reduced when using a laminated iron core)
Not all flux passes through secondary coil. - 43Problems with Rutherford's atom modelThe electron spiral in a perfect circle whilst being attracted to the nucleus
mv²/r = kq₁q₂ / r²
electron is accelerating as its always moving in a circle.
This means that it emits EM radiation
Energy is lost
Electron would spiral into the nucleus in 1 ns - 44What is the cyclotron frequencyBq / 2πm
However
particles can reach 99% c so the relatavistic effect starts to matter. m increases
÷√(1-v²/c²) - 45What is the highest velocity at which a car can go over a hill and not lose contactmv² / r = mg
v = √gr - 46How does a lineac workReference to electric fields
Any three from
particles accelerate when in the gaps
polarity reverses while particles are in the tube
supply has a constant frequency
(Drift) tubes get longer so particles are in tubes for the same half-cycle as speeds are higher
or
see copy's notes - 47How can you calculate the acceleration of a particle in an uniform electric fieldE = F/q
F = ma
a= qE/m - 48What is an important equation linking energy and wave lengthE = hf
λ=h/mv - 49Explain how a EMF is inducedChange in magnetic flux as a result EMF is induced. EMF is dependant on the rate of change of flux linkage. when magnet is stationary. EMF is 0 Volts. Induced EMF is dependant of the direction of the magnet
- 50How is a capacitor chargedA capacitor consists of two parallel conducting plates separated by an insulator.
When it is connected to a voltage supply charge flows onto the capacitor plates until the potential difference across them is the same as that of the supply. The charge flow and the final charge on each plate is shown in the diagram.
When a capacitor is charging, charge flows in all parts of the circuit except between the plates.
As the capacitor charges:
#charge –Q flows onto the plate connected to the negative terminal of the supply.
#charge –Q flows off the plate connected to the positive terminal of the supply, leaving it with charge +Q
#the capacitor plates always have the same quantity of charge, but of the opposite sign
#no charge flows between the plates of the capacitor.
- 51Describe how a cyclotron accelerates a protonElectric field provides a force on the proton
Protons accelerated by electric field between the dees
The electric field is only across the gaps
The magnetic field is perpendicular to proton motion
acts as a centripetal force
The electric field of the dees has reversed when the proton reaches the gap again, polarity switched every half cycle.
constant frequency
(Each successive half-circle) path of the proton has a greater momentun. Radius of circle increases as particles get faster - 52Describe the graph of EMF induced when a magnet FALLS through a coilThe magnitude of (induced) e.m.f. is proportional to the rate of change of Magnetic Flux linkage
When the magnet enters the coil,the change of magnetic flux increases and hence emf increases. At some point, the magnet reaches the middle of the coil. At this point, the amount of flux added to the top half of the coil by the motion of the magnet is equal to the amount of flux removed from the bottom half. Therefore, at this point the EMF is zero.As the magnet leaves the coil,emf is induced in the opposite direction and increases.The polarity of emf changes since the direction of an induced emf is such as to oppose the change creating it(Lenz's Law)
As magnet's speed increases as it falls,
Negative (max) value > Positive (max) value
Or Time for second pulse shorter
The areas of the two parts of the graph will be the same (since Nφ constant)/Flux Linkage is constant - 53Describe the decay of a photon into a proton positron pairOnly charged particles leave a trail so photon is neutral
Particles are oppositely charged because they curve/spiral in opposite directions
APLY FLHR
Because they have the same curvature/radius on the spirals Particles have the same momentum - 54why is energy needed to move charged particles through electric fieldsWork must be done against the repulsive force
- 55Describe and explain the shape of the grap of a discharging capacitorexponential decay, Current decreases by equal fractions in equal time intervals
These graphs show the charge on the capacitor approaching a final value, zero in the case of the capacitor discharging,
but never quite getting there.
The rate at which the charge on a capacitor changes depends on the time constant of the charging or discharging
circuit. - 56André Ampere observed that two parallel wires attract each other if they are carrying current in the same direction. Explain André Ampere's observation.Current in a wire produces a magnetic field
Use right hand rule and draw in magnetic field
(Each) wire is in the magnetic field of the other wire
A current-carrying wire in a magnetic field experiences a force
Mention of Fleming's left hand rule - 57Explain why very high energies are required to produce high mass particles when colliding protonsMass-energy is conserved
(High energy required) to create particles with large/larger mass
because ΔE = c² Δm and c² is a large multiplying factor
There are (electrostatic) repulsive forces between protons
(and high energies are required) so repulsive force can be overcome
to allow protons to get close to each other - 58Whilst moving, empty fuel tanks can be ejected by means of an explosion. This has the effect of increasing the speed of the probe. Discuss whether conservation of momentum and conservation of energy apply in this situation and why the speed of the probe increases.statement that indicates that the conservation of momentum does apply
the idea that the probe and tank move in opposite directions [accept move apart]
Probe and tank experience equal changes in momentum (in opposite directions)
Statement that indicates that (total) energy is conserved
Kinetic energy of the system increases (so speed increases)
(Some) chemical energy converted to KE - 59Use an equation to explain whether the time taken for the capacitor to lose half its energy is greater or less than the time taken to lose half its charge.Refers to W = QV/2
Q and V both decrease over time
W will decrease faster so takes less time to half in value. - 60Explain the significance of the minus sign in lenz's law-It states that the induced current
-opposes the change that produces it - 61Explain how an EMF is produced when AC current passes through clamp meter-the alternating current produces an alternating magnetic field
-the iron core is magnetised
-in which the field is linked to the coil of wire
-EMF is produced due to EM induction - 62Explain, with reference to lenz's law, how a magnet does work as it enters a coil.- lenz's law states that the direction of induced EMF is such to oppose the change creating it.
-the induced current in the coil pr duces a magnetic force to oppose the motion
-so there is a force acting on the magnet in the opposite direction to its motion
-As work = force x distance, work is done as the magnet moves - 63Why is a diode needed if the battery is to charge? (Rechargeable torch by shaking)-alternating current is produced
-so without diode, the diode would charge and discharge. - 64List of vectorsDisplacement
Velocity
Acceleration
Force
Weight - 65List of scalarsSpeed
Distance
Time
Mass
Energy - 66What effect does a current carrying wire have?A current carrying wire has a magnetic field. The larger the current, the stronger the field.
- 67How can the magnetic field around a solenoid be increased?Increase the current, increase the number of turns (coils), decrease the cross-sectional area of the solenoid (same number of turns), decrease the length of the solenoid (same number of turns), add an iron core inside the solenoid.
- 68How do you calculate the force acting on a current carrying conductor in a magnetic field?Force on a conductor = magnetic flux density (T) x Current (A) x length (m) or F = B x I x L
- 69The motor effect happens when a charged particle moving at right angles to a magnetic field feels a force on it at right angles to the direction of motion and also at right angles to the field.This Force,F is calculated by...F=Bqv
or
F=Bevsinθ - 70How do motors work?In DC motors, a current carrying coil sits between two opposite poles of a magnet. The current is flowing in different directions on each side of the coil, and each side of the coil is perpendicular to the magnetic field, each side experiences a force in the opposite direction. The coil is on a spindle, and the forces are in opposite directions, so it spins. The split ring commutator swaps the contacts every half turn, keeping it spinning in the same direction. If you swap the polarity of the dc supply, the motor will spin the other way. The direction the motor turns can be found out using Flemings left-hand rule.
- 71How do loud speakers work?A loudspeaker has a coil of wire surrounded by a magnet. There is also a magnet inside the coil. Ac electrical signals are fed into the coil of wire, which is wrapped around the base of a cone. The interaction between the magnetic field and the current in the coil forces the coil to move in one direction. As it is an alternating current, the current changes direction, forcing the coil back in the other direction, making the coil move back and forth, vibrating and producing a sound.
- 72What is the transformer equation?
- 73The charge, Q, on a capacitor of capacitance C, remaining time t after starting to discharge is given by the expressionQ = Q0e–t /τ where Q0 is the initial charge on the capacitor
This expression shows that when t is equal to τ, i.e. after one time constant has elapsed, the charge remaining is equal to Q0e–1, or Q0/e - 74Important Current FormulaI=C*dv/dt
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- Physical Sciences Fichas sobre Physics Unit 4, creado por Leichombam Singha el 10/05/2019.
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- Leichombam Singha
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