p4 Flashcards
1
Q
- e- replaced by alpha-particle, same speed
describe and explain the shape of the path in the region of the MF and EF
A
- staright line without deviation bcuz the deflection
depends on speed. - since speed remain constant, the Fm remain constant
- deflection does not depend on mass and charge
2
Q
1 function of a transformer
A
to change the magnitude of pd
3
Q
Use Faraday’s Laws to explain why the output from the transformer is an emf that is alternating
A
- Magnitude of emf △ as the rate of △ of
magnetic flux △ - the direction of emf △ when the direction of △ of
magnetic flux reverses - the flux is continuously inc and dec, hence polarity of
the emf is continuously switching
4
Q
state why the soft iron core of the transformer is laminated
A
to reduce the size of eddy current in the core so that E losses in the core due to heating is reduced
5
Q
Suggest why a nucleus of He-4 does not spontaneously break down to become nuclei of H
A
- The binding energy per nucleon is much greater
- therefore It requires a large amount of energy to
separate the nucleon in helium
6
Q
3 functions of capacitors
A
- to block direct current
- time delaying
- soothing effect
- oscillator
7
Q
By ref to yr ans, suggest why Hall probes are usually made using semiconductors rather than metals
A
- VH is inversely proportional to n
- semiconductors have a smaller value of n.
- Therefore, Vh for semiconductors is larger, so more
easily measured
8
Q
Explain how this current give rise to an induced electromotive force (emf) in the secondary coil
A
- alternating current creates a changing magnetic flux
- the magnetic flux is linked to the secondary coil through
the soft iron core - the secondary coil cuts across the magnetic flux.
- changing magnetic flux takes takes
- current and emf are induced
9
Q
Explain why the NR on the mass will have diff values at the equator and at the poles
A
(at poles) Fc = Fg - NR
since Fc is zero (cuz its stationary with no orbit path, r=o)
NR = Fg
- As the mass moves away from the equator, the orbit r ↓
- the Fc (mrw^2) is no longer parallel to Fg (GMm/R^2)
10
Q
Suggest 2 factors that could, in the case of a real planet, cause variations in a of free fall at its surface
A
ref: F=ma
GMm/r^2 = ma
- radius of planet varies
- density of planet is not constant
- spinning of planet
11
Q
explain why the gravitational potential near an isolated mass is always negative
A
- the gravitational potential at infinity is zero
- gravitational force is always attractive so,
- work got out as mass is moved from infinity to that point
12
Q
Suggest why, for small changes in height near earth’s surface, gravitational potential is approx constant
A
- r of earth is much greater than height
- gravitational potential is inversely proportional to the r
- since height is very small, r is constant, gravitational
potential is approx constant
13
Q
explain why, at the surface of a planet, gravitational field strength is numerically equal to the acceleration of free fall
A
- acceleration = F/m
- gravitational field strength = F/m
- therefore the grav field strength is equal to a of free fall
14
Q
By ref to the lines of gravitational force near to the surface of the earth, explain why the gravitational field STRENGT g close to the earth’s surface is approx constant.
A
- near the surface, earth has a large radius compared to the height above surface.
- so radial lines of force are almost parallel
- field strength is approx constant
15
Q
2 wires are now placed through a card. The 2 wires are parallel and carrying currents in the same direction.
Explain why a magnetic force is exerted on each wire
A
- Current in each wire creates a magnetic field at the
other wire. - The current in wire at 90 ° to field produces force
16
Q
state 2 other observations associated with photoelectric emission that provide evidence for a particular nature of electromagnetic radiation
A
- max KE of e- is independent of intensity
- max KE of e- depends on the frequency
- intensity is proportional to the rate of photons emitted
17
Q
Rockets on satellite are fired for a short time. The satellite is now closer to the surface of the planet.
State and Explain the change to the Ek of the satellite
A
- v^2 ∝ 1/r
- when r ↓, speed ↑
- hence Ek of satellite ↑
18
Q
- The acceleration a of the tube is given by the -
expression a = - (Aρg/m)x , where x is vertical
displacement - Use the expression to explain why the tube undergoes
simple harmonic oscillations in the liquid
A
- acceleration is ∝ to displacement
- (-ve) sign indicates that displacement and acceleration
are in opp directions - A, ρ, g and m are constant
19
Q
State 3 features of the orbit of a geostationary satellite
A
- orbits from west to east
- period of 24 hours
- above the equator
20
Q
ads and disads of geostationary satellite
A
ads: no tracking required
disads: longer time delay
21
Q
Use laws of electromagnetic induction to explain why when the switch is closed, the current ↑ GRADUALLY to max value
A
- Increasing I cause increasing magnetic flux
- Increasing flux induces an emf in the coil
- Induced emf opposes the growth of I due to Lenz’s law
22
Q
Explain why, although charge A is a point charge, the electric field strength btw 3-7cm does NOT obey inverse square law
A
- Field is due to both charge
- Charge A is not isolated
23
Q
Functions of capacitors in electrical circuits
A
- To store electrical energy
- To block direct currents
- Time delay circuuits
24
Q
State 3 pieces of evidence provided by the photoelectric effect for a particular nature of electromagnetic induction
A
- Max E of emitted e- depend on freq
- Max E of emitted e- independent to intensity
- rate of emission of e- depends on intensity
25
Suggest why the total activity of the radioactive source measured at the time calculated in (i) may be greater than 0.40 A0
- daughter product may be radioactive
or
- random nature of decay
26
Explain why planet A may be assumed to be a point mass when viewed from planet B
- Size or diameter of planet A is much smaller than
| separation of planets A and B
27
Example of uses of resonance effect
- microwave ovens
- MRI
- quartz crystal to produce ultrasound
28
State and explain, if any, on the polarity of the Hall voltage when -ve charge carriers (e-) are replaced with +ve charge carriers, moving in the same direction towards the slice
- the +ve and -ve charge would deflect in opp directions
| - so no change in polarity
29
Brownian motion of the smoke particles is seen through a microscope. Describe;
i) what is seen thru the microscope
ii) how Brownian motion provides evidence for
the nature of the movement of gas molecules
i) specks of light moving haphazardly
ii) gas molecules move randomly and collide with smoke
particles. This cause the smoke particles to change
directions
30
Explain why, although the power of the heater is changed, the rate at which thermal energy is transferred from surroundings to ice is CONSTANT
- Temperature difference btw apparatus and surroundings
| does not change
31
Explain why most of the emitted e- will have a v lower than Vmax
- E is required to bring e- to the surface
32
Use one of the assumptions of the KE theory of gases, to explain why the Ep of the molecules of an ideal gas is zero
- There are no intermolecular forces btw molecules, so no
| Ep
33
During MELTING process, a solid becomes liquid with little to no change in volume.
Use KE theory to explain why, during the melting process, thermal E is required although there is no change in Temperature
- During melting, bonds btw molecules are being
broken
- Ep of molecules is ↑, Ek remain constant
- Little to no work done is required
- Therefore the required input of E is thermal E
34
A distant star is orbited by several planets.
i) Each planet is at constant speed. Explain whether the
planets are in EQUILIBRIUM.
- they r not in equilibrium bcuz the direction of motion is
| changing with acceleration
35
Explain why, for an ideal gas, the change in internal E is directly proportional to the change in thermodynamic temperature of gas.
- In ideal gas, the Ep is 0 because the IMF btw molecules
is negligible
- Internal E is equal to the KE of molecules
- KE is proportional to the thermodynamic temperature of
gas
36
An aluminum ring is placed on the core. The ring can move freely along the length of the core.
Use Faraday's law and Lenz's law to explain why the aluminium ring jumps upwards when switch is closed.
- When switch is closed, current passes thru the coil and
produce magnetic flux.
- Aluminium ring will cut across the magnetic flux
- changing magnetic flux takes place, emf and current
are induced
- Current in the ring will produce field around aluminium
ring
- Based on Lenz's law, the field around the aluminium ring
opposes the field around the coil
37
a = -(2g/L)x
| Show that the liquid column undergoes simple harmonic motion
- g and L are constant
- a = -kx
- therefore, acceleration is proportional to displacement
- acceleration and displacement are in opposite
directions
38
---- liquid column
| Suggest 1 cause of damping of oscillations
- viscosity of liquid
- friction within liquid
- friction btw wallas of tube and liquid
39
State the relationship between electric field at a point and electric field strength at the point
Electric field strength = - potential gradient
Negative sign shows that electric field strength acts in
direction of decreasing potential gradient
40
Describe the appearance of a visible line emission spectrum, as seen using a diffraction grating
- dark background
| - coloured lines
41
During the change from B to C, the internal energy of the gas decreases by 313J.
By considering molecular energy, state and explain qualitatively the change, if any, in the temperature of the gas.
- in ideal gas, Ep is zero
- no IMF btw gas molecules
- since internal ↓, Ek ↓,
- temperature ↓
42
Permanent magnets are now positioned so that the metal block oscillates btw the poles.
Use energy of conservation to explain why the energy of the oscillations decreases more rapidly than before,
- metal block cuts across magnetic flux produced by the
permanent magnets
- changing of magnetic flux takes place
- emf and current are induced in the block
- eddy current induced in the block produces heating
- heat energy of eddy current comes from the energy of
oscillations
43
State 1 similarity and 1 diff btw the electric field lines and gravitational field line ard an isolated positively charges metal sphere
similarity - both lines are radial
difference - gravitational field lines are directed towards
sphere and electric field lines are directed
away from sphere
44
(+Q)A------------------------------------B(+Q)
A small +ve charge is placed at A. The electric field causes this charge to move from rest along the line AB
Describe the acceleration of the charge as it moves from A to B
- Acceleration ↓ to zero at midpoint and then ↑ in opposite direction
45
Explain why speed of the particle is not affected by the magnetic field
- The F on the particle is always ppd to its velocity.
- No work is done by the F on particle
- No acceleration in the direction of velocity
46
Ideal transformer is shown.
Explain:
ii) why an emf is NOT induced at the output when a
constant direct voltage is at the input
ii) - emf is only induced when the magnetic flux is
changing
- direct current gives constant flux
47
Ideal transformer is shown.
Explain:
i) why is the core made of iron
i) to ↑ magnetic flux linkage w secondary coil
48
All of the light absorbed by the hydrogen is re-emitted. Explain why dark lines are still observed in the absorption spectrum
- Because light is re-emitted in all directions when
| passing thru diffraction grating
49
State and explain whether the energy of the gamma-ray photon is equal to the E released in the reaction.
- the product nucleus has kinetic energy.
- therefore, the gamma-ray photon will have less E than
the total E released
50
escribe the motion of molecules in a gas, according to the KE theory of gas
- molecules move randomly in all directions
51
In an α-particle scattering experiment, the beam of α-particles is incident on a very thin gold foil.
Suggest why the gold foil must be very thin
- so that single interactions between nucleus and α-
| particle can be studied
52
By ref to the action of a transformer, explain why the input to the transformer is an alternating voltage, rather than a constant voltage
- With an alternating voltage, a changing magnetic flux is
produced in the iron core
- Changing magnetic flux is linked to the secondary coil
- emf and current in secondary coil are only induced
when flux is changing
53
The spectrum of the light emerging from the cloud of cool gas is viewed using a diffraction grating.
Explain why this spectrum contains a number of dark lines
- e- in the gas interacts with photons.
- e- absorbs the photon E and gets excited from ↓ to ↑ E
levels
- Photon absorbed is equal to the diff in E levels
- The e- r unstable and fall back to lower E level.
- When e- de-excites, photons will be emitted in all
directions, dark lines are formed
54
A large container is filled with ideal gas
| Explain how movement of the gas molecules causes pressure in the container.
- Molecules collide with walls of container
- Change in momentum btw molecules and wall is
produced
- F = (mv-mu)/t , time is constant, force is produced on
molecules and wall
- Many forces act over surface area of container, exerting
a pressure
55
[circuit with resistor connected to coil (with magnet-spring oscillating)]
The switch is now closed. Explain why the oscillations of the magnet are damped
- When switch is closed, the current flow through the coil
and produce magnetic flux
- The two fields cause an opposing force on magnet
- Thermal energy is dissipated in resistor
- Thermal energy comes from energy of magnet
56
Explain why the e- follow a circular path when inside the region of the magnetic field.
- F is always normal to direction of motion
- Magnetic F provides Centripetal F
- Magnitude of magnetic F is constant.
- No work is done by the F on particle
57
State the measurements needed to determine the c/m of an electron
- accelerating pd
- radius of path
- magnetic flux density
58
Sinusoidal vs Square V/t graph
- State and explain whether the same power would be
dissipated in a 1.0ohm resistor connected to each
supply.
- No, bcuz the rms voltages are diff
59
State 1 reason why the transformer is not 100% efficient
- E losses due to resistance of coil
- E losses in magnetision and demagnetision
- E losses due to eddy current
60
The intensity of the electromagnetic radiation for 1 particular freq is ↑
State and explain the change, if any
i) Max KE of emitted e-
ii) rate of emission of photoelectrons
i) Each photon has same E, so no change
ii) More photons emitted per unit time, so rate of
emission ↑
61
By ref to the IMF, explain why the change in internal E of an ideal gas is equal to the change in total KE of its molecules
- In ideal gas, there is no IMF btw molecules.
- Ep is zero
- Therefore △ in KE is equal to △ in Internal E
62
State and explain the △, if any in the internal E of a solid metal ball as it falls under gravity
- ↓ in total Ep = ↑ in total KE
- No extra E is supplied.
- Therefore, no △ in internal E
63
Aluminium disc supported horizontally and held stationary. Magnet is rotated about the vertical axis at cons speed.
Use laws of electromagnetic induction to explain why there is a torque acting on the aluminium disc
- The aluminium disc will cut across the magnetic flux of the magnet
- △ in magnetic flux takes place, emf and current r induced
- Emf causes eddy current in the disc to oppose the △ in flux, and produces magnetic force on the aluminium disc
64
1. PV = Nmv^2
2. p = 1/3ρ
Explain how each of the following terms in eqn 2 is derived from eqn 1
i) ρ
ii) 1/3
iii)
i) ρ - Nm/V
ii) 1/3 - molecules move in 3 dimensions. So 1/3 in any
directions
iii) - Molecules have diff speeds, so take ave of
(speed)^2
65
1st law of thermodynamics exp, if any, △in the internal E :
a) a lump of solid a constant T
b) Toy balloon bursts, no thermal enters/leaves gas
a) - little to no wd
- thermal E is supplied to provide latent heat
- internal E ↑
b) - V ↑, Wd against atmosphere
- internal E ↓
66
Why the emf induced in the secondary coil is not constant
- rate of change of magnetic flux is not const
| - emf is prop to rate of change of magnetic flux
67
Suggest why the E required to launch the satellite depends on whether satellite, in its orbit, is travelling from west to east of east to west
- earth's rotation is from west to east
- smaller gain in E if orbit is in the same direction as
Earth's rotation
68
Suggest why, when the capacitor is connected across the terminals of a battery, the capacitor stores energy, not charge.
- The charges on each plate are equal in magnitude and
opposite to each other, no resultant charge
- +ve & -ve charges are separated, so E is stored
69
State the basic principle by which temp is measured
- using a thermometric property.
| - V ↑ with Temp
70
By ref to using a thermometric property to measure temp, explain why 2 thermometers may not give the same temp reading for an object
- physical properties may not vary linearly w temp
| - temp scale assumes linear change of property w temp
71
The mean value of an alternating current is zero.
| Explain why heating occurs when there is an alternating current in the resistor
(P=I^2R)
- heating depends on (current)^2 and (current)^2 is always +ve
72
Transmission of electrical E is frequently achieved using alternating high voltages.
i) Why are high voltages used.
ii) Why voltage is alternating
i)- With ↑ voltage, current flow is low
- With low current flow, power loss due to heating during energy transmission is low
ii)- The voltage can be easily stepped ↑ or ↓
or - The transformer only works with alternating current
73
For any point outside a spherical conductor, the charge on sphere may be considered to act as a point charge at its centre. By ref to electric field lines, explain this
- Electric field lines are radial
| - Electric field lines APPEAR to originate from the centre of the sphere
74
Explain why a constant VH is developed btw the faces you have named in (i)
- charge carrier moving normal to magnetic field
- charge carrier experiences a F normal to current and magnetic field
- Charge build-up set up an Fe across the slice
- Charge stop building up and becomes constant when the Fm is equal in magnitude but opp in directions to Fe
75
Wavelength ↓, constant intensity,
| State and explain the effect, if any, on the photoelectric current.
- when wavelength ↓ at constant intensity,
- freq of photon ↑ (v=fλ)
- no. of phton per unit time ↓ as the intensity is constant
- less e- per unit time
- photoelectric current ↓
76
State 3 reasons why the activity of the sample of copper-66 is not equal to the measured count rate.
- Background radiation is measured
- Radiation emitted in all directions
- Daughter products are radioactive
77
The y-ray photons emitted from radioactive nuclei have specific energies, dependent on the nucleus emitting photons.
By comparison, w emission line spectra, suggest what can be deduced about energy levels in nuclei
- discrete energy levels in nuclei
78
The stars are in circular orbits w the centres of both orbits at point P.
Explain why the centripetal force acting on both stars have the same magnitude.
- Gravitational force provides centripetal force.
| - Based on Newton's 3rd Law, both spheres have same magnitudes of gravitational force
79
Suggest a suitable thermometer
i) temp of flame of bunsen burner
ii) △in temp of small crystal when its exposed to a pule of ultrasound energy
i) thermocouple/ pyrometer
| ii) thermistor
80
In some semiconducting materials, e- are mainly responsible for conduction. In other semiconducting materials, holes are mainly responsible for conduction.
Suggest and explain the difference, if any, that conduction by e- or by holes will have on the Hall voltage.
- magnetic field would deflect holes and e- in same directions
- e- are -ve and holes are +ve
- so Vh have opp polarity
81
Suggest why the electric field strength in both spheres is zero.
- In electric field, charges in conductor would move.
| - Since no movement of charges in sphere, no Rf on charges, so E=0
82
State Power losses within a transformer
- heating due to eddy currents induced in core
- heating due to current in resistance of coils
- power loss due to changing magnetic field in core
83
State an effect that provides evidence for
i) wave nature of particle
ii) particular nature of electromagnetic radiation
i) e- diffraction
| ii) photoelectric effect
84
Explain why the magnitude of the final momentum of the e- is not equal to the △ in magnitude of the momentum of the photon.
- momentum is vector quantity
- so we need to consider the △ in direction, not just magnitude
- we must consider momentum in 2 directions
85
- As the magnet is being moved into the solenoid, thermal E is transferred in the resistor.
- Use laws of electromagnetic induction to explain the origin of this thermal E
(4)
- emf ∝ nba/t
- as magnet moved into solenoid , solenoid cuts thru magnetic flux of magnet
- △ in magnetic flux takes place, emf and current are induced in solenoid
- current in solenoid produces field around solenoid and opposes the field around magnet.
- work is done to move magnet into solenoid
- induced current gives heating effect in resistor which comes form the work done
86
Explain why the alternating current in the primary coil of the transformer is NOT IN PHASE w the alternating emf induced in the secondary coil.
- current in primary coil give rise to a magnetic field
- magnetic field in core is IN PHASE w the current in the primary coil
- this magnetic flux cuts thru the 2nd coil, △ in magnetic flux takes place. emf is induced in 2nd coil, which is ∝ to rate of change of magnetic flux, hence not in phase
87
Distinguish for an atom, btw a nucleus and nucleon
nucleus - small central core of an atom
| nucleon - total no. of p and n in a particle within a nucleus
88
- A capacitor w a large capacitance is connected across the terminals of the supply.
- Suggest and explain why this may lead to a large current from supply.
- a large charge required to charge capacitor
- capacitor would charge and discharge rapidly
- I = Q/t , so large I produced
