# Physics Paper Options and Explanations

The Matrix 2020 HSC Physics Examination Paper Options are right here! The Matrix Science group has been arduous at work on them.

## Part 1: A number of Alternative

 Query Reply Answer 1 D Huygens proposed that mild propagated by way of the formation of wavelets. 2 A An AC motor has no brushes as present is utilized to the stator. Strictly talking, an AC induction motor doesn’t require present to be provided to the rotor as a substitute, the present within the rotor is induced by the altering stator discipline. 3 C Maxwell was a theorist who confirmed that altering magnetic fields may induce electrical fields and vice versa, leading to electromagnetic waves. 4 B In line with the graph, the half-life is about 100 years (time when the remaining mass is half of the beginning worth). (lambda = frac{textual content{ln }2}{100} = 0.0069 textual content{ years}^{-1}) 5 B The preliminary vertical element of velocity  determines the time of flight based on the equation (s_y = u_y t + frac{1}{2}at^2). 6 A The celebrities range in color as indicated by the x-axis. Additionally they range in luminosity, as indicated by their magnitude on the y-axis. These components point out that additionally they range in mass. Being a part of a cluster means that they’ve roughly the identical age. There are long-lived crimson important sequence stars and the bigger stars have moved on to being giants or white dwarfs 7 D The output proven is that of a DC generator, which makes use of a split-ring commutator to transform alternating present within the coil to pulsed direct present within the exterior circuit. 8 C The method reduces each the mass quantity and atomic quantity by 2, so it should contain the emission of an alpha particle. The ingredient with atomic quantity 90 is thorium. 9 A The Bohr mannequin was the primary to include discrete power ranges, which defined why solely sure wavelengths have been produced in a component’s emission spectrum. 10 B The underside plate have to be positively charged to exert the electrical power proven, so the electrical discipline factors in direction of the highest of the web page. In line with the RH palm rule, a magnetic discipline out of the web page could be required to provide an opposing power upwards. 11 C The ultimate mass is smaller than the preliminary mass, so mass has been transformed to power and launched. This response is a transmutation reasonably than a fusion, because it doesn’t mix two nuclei. 12 D The escape velocity doesn’t depend upon the mass of the satellite tv for pc, however does depend upon preliminary place as given by (v_{esc} = sqrt{frac{2Gm}{r}}).  The shut the satellite tv for pc is to Earth, the smaller the worth of (r) and the larger the escape velocity. 13 A Studying from the graph tells us that electrons from steel Y may have a decrease most kinetic power. This corresponds to their most velocity additionally being decrease. 14 C Reversing the present will outcome within the wires being attracted to one another. Doubling the present in Y will outcome within the magnitude of power doubling, based on Ampere’s Legislation. 15 D If the rocket is initially travelling horizontally at a relentless velocity of (20 textual content{ ms}^{-1}), there will need to have been zero web power on it. At the moment, the thrust will need to have been equal to the rocket’s weight: (w = mg = 7800 occasions 9.8 = 76440 textual content{ N}). When the thrust is elevated to (90000 textual content{ N}) there will likely be a web power upwards, and therefore an acceleration upwards. 16 A The query signifies that the moderator will increase the speed of fission, so its loss will trigger the speed of fission to lower. Withdrawing the management rods will improve the speed of fission as fewer neutrons are absorbed. 17 C Observer Y sees the carriage as being size contracted, so the space from the supply to the sensor is diminished. Since each observers should agree on the velocity of sunshine, Y sees it take a shorter time than X to achieve the sensor. 18 B When the Earth is travelling away from Jupiter, the sunshine sign from the beginning of 1 orbit will take longer to achieve Earth than the sunshine sign from the beginning of the earlier orbit,  because it must journey an extended distance to achieve Earth. Due to this fact the interval will seem like longer. 19 C Within the beginning place proven, prices within the conductor are all transferring to the best, parallel to the magnetic discipline. They don’t expertise a magnetic power, so there isn’t any EMF. After 1 / 4 of a flip, when the conductor is horizontal, all the costs will likely be transferring vertically (perpendicular to the sphere). They expertise a magnetic power: optimistic prices are pushed into the web page and unfavourable prices are pushed out of the web page. This doesn’t end in a cost separation throughout P and Q, and doesn’t produce an EMF between them. 20 A This query combines features of projectile and round movement. There’s a fixed downwards power as a result of weight which is fixed. Within the horizontal airplane the ball is in uniform round movement. The horizontal, centripetal power from the wall (F_c = frac{mv^2}{r}) stays fixed for the reason that ball’s horizontal velocity stays fixed. These two forces stay perpendicular to one another, so the magnitude of their sum stays fixed.

## Part 2: Brief Response

### Query 21 ( 5 marks)

(a) Use the Rydberg equation:

(frac{1}{lambda} = R_H left(frac{1}{n_f^2}-frac{1}{n_i^2} proper) = 1.097times 10^7 occasions left(frac{1}{2^2} – frac{1}{3^2}proper)) which provides (lambda = 656 textual content{ nm})

(b) Electrons within the Bohr mannequin exist in certainly one of a variety of secure power states. They will solely transition to a better power state by absorbing the precise power wanted from a photon, and may solely transition to a decrease power state by releasing the surplus power by the emission of a photon. The entire power earlier than and after the transition have to be the identical as said by the Legislation of Conservation of Power.

### Query 22  (5 marks)

(a)  The height wavelength is calculated utilizing Wien’s Displacement Legislation.

( lambda = frac{b}{T} = frac{2.898times 10^{-3}}{3200} = 9.056 occasions 10^{-7} textual content{ m} = 906 textual content{ nm} )

(b)  Particular Relativity solely has measurable results when the capsule is transferring near the velocity of sunshine. Even its most velocity is just a tiny fraction of the velocity of sunshine and the consequences will likely be undetectable.

The capsule can be accelerating, so it’s not an inertial body of reference and can’t be analysed utilizing Particular Relativity.

### Query 23 (3 marks)

When the motor produces a torque of (2.95 textual content{ Nm}), we are able to learn from the graph that the angular velocity is roughly (100 textual content{ rads}^{-1}). Utilizing these values, we are able to rearrange the torque equation and calculate the present:

( I = frac{omega tau}{eta V} = frac{100 occasions 2.95}{0.3 occasions 240} = 4.10 textual content{ A})

This present is beneath the utmost allowed worth, so the circuit breaker is just not wanted and the motor can function.

### Query 24 (4 marks)

In an effort to calculate the projectile’s preliminary velocity, we’d like each the horizontal and vertical elements of the rate.

We will calculate the horizontal velocity utilizing the said vary and the time of flight.

(u_x = frac{s_x}{t} = frac{130}{6} = 21.7 textual content{ ms}^{-1})

In an effort to discover the preliminary vertical velocity, we are able to use the truth that the utmost vertical displacement was reached after three seconds, at which level the vertical velocity could be zero.

( v_y = u_y + at)

( 0 = u_y + (-9.8) occasions 3 )

( u_y = 29.4 textual content{ ms}^{-1} )

The ultimate velocity is the vector sum of the elements, which is ( 36.5 textual content{ ms}^{-1}) at ( 54^circ ) above the horizontal.

### Query 25 (4 marks)

The hydrogen atom consists of 1 proton and one electron.

The electron is a lepton, an elementary particle.

The proton consists of three quarks, two up and one down. The quarks are held collectively by the robust nuclear power, which is mediated by gauge bosons often known as gluons.

The electron orbits the proton as a result of electromagnetic power which ends up in attraction between then, which is mediated by digital photons.

### Query 26 (8 marks

(a) A gasoline discharge tube will produce a spectrum composed of strains at discrete wavelengths (which can depend upon the power ranges of the gasoline within the tube). An incandescent lamp produces a continuum spectrum, a black physique spectrum, with the height emission wavelength depending on its temperature.

(b) Mannequin X assumes {that a} black physique radiates equally in any respect frequencies.

Mannequin Y assumes that the radiation is emitted in power packets, the place the frequency of emission is proportional to the power of a transition (i.e. to the power carried by the packet being emitted). Some transitions are inconceivable and others happen with various likelihood.

(c)  The curve for the ( 4000 textual content{ Okay} ) black physique may have a decrease depth in any respect wavelengths, as a result of the full energy emitted by a physique decreases as temperature decreases. The curve may also have its peak at an extended wavelength (which needs to be calculated by Wien’s Displacement Legislation: ( lambda = 725 textual content{ nm} )). It is because the likelihood of sure power transitions occurring varies with temperature. Smaller power transitions are extra frequent at decrease temperatures, the place the typical power per particle is decrease, and these correspond to the emission of longer wavelength photons as ( E = hf = frac{hc}{lambda}).

### Query 27 (4 marks)

The gap between maxima is set by the wavelength of sunshine but additionally by the space between the slits and the space to the display screen.

When the wavelength ( lambda ) is diminished, the spacing of the maxima reduces based on  (d textual content{sin} theta = m lambda ). There’s a lower within the angular separation. In an effort to convey the spacing again to its authentic worth, we are able to lower the separation between the slits ( d ), inflicting ( theta ) to extend, or we are able to place the display screen additional away from the slits by growing ( y ), inflicting their linear separation to extend.

### Query 28 (7 marks)

(a) The magnetic flux by the loop is ( Phi = BA textual content{cos} theta).

The sphere power is fixed at (1 textual content{ T}), the angle between the sphere and the realm regular vector is (30^circ ), and the realm will shrink by (0.3 textual content{ m} occasions 0.2 textual content{ m}) when the rod is moved. This provides the change in flux:

( Delta Phi = B textual content{cos} theta occasions Delta A = 1 occasions textual content{cos}30^circ occasions 0.3 occasions 0.2 = 0.052 textual content{ Wb} )

(varepsilon = – frac{Delta Phi}{Delta t} = – frac{-0.052}{2.5} = 0.021 textual content{ V} )

(The change in flux is taken to be unfavourable, since it’s a lower of flux.)

The present will move anticlockwise as considered from above. (It is because the upwards flux by the loop is reducing, so the loop tries to generate further flux upwards, based on Lenz’s Legislation.)

(c)  There may be at all times a gravitational power pulling downwards on the rod. The downhill element of that have to be overcome to maneuver the rod as described within the query. Moreover, when the magnetic discipline is current, the induced present tends to provide a power opposing the movement based on Lenz’s Legislation. This makes it tougher to maneuver the rod as you should overcome each forces.

With out the magnetic discipline, the opposing power because of Lenz’s Legislation is just not current and so much less power is required to maneuver the rod, as solely the downhill element of the gravitational power have to be overcome.

### Query 29 (5 marks)

(a)  Gamma rays have been identified to have zero electrical cost, which might clarify their lack of deflection in an electrical discipline. They have been additionally identified to hold power, which might be transferred to protons within the paraffin to eject them. Nonetheless, gamma rays could be able to producing the photoelectric impact as they’re excessive power photons, so this disagrees with observations.

Scientists additionally discovered that the power related to gamma rays was not ample to eject the protons with the velocities noticed, apparently violating conservation of power.

(b) These experiments confirmed the existence of the neutron, which have been the unknown radiation talked about within the query. This allowed scientists to appropriately establish the composition of the atomic nucleus – that it was composed of protons and neutrons in particular ratios.

### Query 30 (7 marks)

(a) Power may be transformed to mass based on Particular Relativity. By accelerating particles to excessive kinetic energies and colliding them, scientists at particle accelerators have been capable of create heavy, unstable particles that weren’t usually noticed on Earth. The existence of those particles, their bodily properties, and their interactions and decay have been used as proof for the Customary Mannequin of matter.

For instance, deep inelastic scattering experiments confirmed that particles might be faraway from protons. This indicated protons usually are not basic and result in the invention of quarks. (Many examples could be acceptable right here.)

(b) (i) Utilizing de Broglie’s equation:

(lambda = frac{h}{mv} = frac{6.626 occasions  10^{-34}}{1.673 occasions 10^{-27} occasions (0.1 occasions 3 occasions 10^8)} = 1.32 occasions 10^{-14} textual content{ m} )

(ii) The relativistic results would end in its wavelength being shorter. The wavelength is inversely proportional to momentum, (lambda = frac{h}{p}) , and, at these speeds, the proton’s relativistic momentum needs to be used which is bigger than its non-relativistic momentum.

### Query 31 (6 marks)

(a)  Kepler’s Second Legislation states that the vector becoming a member of the comet to the Solar will sweep out equal areas in equal occasions. As a consequence, the comet should journey at a better velocity when it’s near the Solar and a decrease velocity when it’s additional away.

Moreover, when the comet is way away from the Solar it has larger potential power, and decrease kinetic power and therefore velocity.

(b)  The one approach for (A) to journey with fixed velocity is that if its orbit is round. This can solely happen if (A) and (B) are each orbiting in a circle round a standard centre of mass, and are at reverse sides of the circle.

The gravitational power on (B) from (A) have to be equal to the centripetal power protecting it in round movement. Since (x) is the space between the celebrities, the radius of the round movement is (frac{x}{2}).

( F_G = F_C )

( frac{Gmm}{x^2} = frac{mv^2}{frac{x}{2}} )

( v = sqrt{frac{Gm}{2x}} )

### Query 32 (7 marks)

In the end the components that restrict the velocity are the ability of the motor and the coefficient of kinetic friction between the mass and the floor it’s sliding on.

The mass will expertise friction given by (f = mu N). For the reason that mass is just not accelerating vertically, the traditional power will likely be equal to its weight, therefore (f = mu mg). The friction have to be balanced by the strain coming from the string (and the motor) for the mass to journey at fixed velocity.

The utmost velocity will likely be decided by the ability of the motor and the power required: (P = Fv = mu mg v).

The power produced by the motor will depend upon its torque and the radius of the pulley, (tau = Fr = mu mg r).

Expressing the mass’s velocity by way of the motor’s angular velocity, (v = r omega) provides:

(v = frac{P}{mu mg} = frac{tau omega}{mu mg}).

The above exhibits that the velocity is proportional to the ability of the motor and inversely proportional to the coefficient of friction.

Potential further dialogue:

The torque in electrical motors is proportional to the present by its coils. This can depend upon each the exterior voltage and the rotation velocity (by the again EMF induced by the rotating coils).

The motor’s most velocity could be that for which the web voltage on the coil permits for ample present and torque to stability the torque on the pulley produced by the friction.

### Query 33 ( marks)

The magnet is stationary at (X), so it has an power of (U = mgh = 0.04 occasions 9.8 occasions 0.98 = 0.38416 textual content{ J}) relative to the underside of the cylinder.

Because the magnet falls beneath the affect of gravity its potential power is transformed to kinetic power. When it reaches the highest of the cylinder, its potential power reduces to (U = 0.04 occasions 9.8 occasions 0.2 = 0.0784 textual content{ J}), and its kinetic power is (Okay = 0.30576 textual content{ j}), such that the full power stays the identical at (0.38416 textual content{ J}).

(An alternative choice: calculate its velocity and therefore kinetic power from the graph, noting that it was falling for (0.4 textual content{ s}).)

The cylinder experiences a change in flux when the magnet begins to move by it, leading to an induced EMF based on Faraday’s Legislation. A present flows across the circumference of the cylinder as a result of it types a closed circuit.

The present produces a magnetic discipline which interacts with the magnet to provide an opposing (upwards) power, based on Lenz’s Legislation.

The opposing power causes the magnet to decelerate, after which fall at fixed velocity as seen within the graph (the power have to be balancing its weight). From the graph, the velocity of the magnet is ( 0.4 textual content{ ms}^{-1}), calculated by taking the gradient of the space vs. time graph.

When the magnet reaches the underside of the cylinder its potential power is 0 and its kinetic power is ( Okay = frac{1}{2} mv^2 = 0.0032 textual content{ J}).

Its preliminary power was (0.38416 textual content{ J}) that means that (0.38416 – 0.0032 = 0.38096 textual content{ J}) have been transformed into {the electrical} power of the induced present within the cylinder, after which to warmth by the copper’s resistance.

The power because of Lenz’s Legislation did unfavourable work on the falling magnet in an effort to scale back its kinetic power.

### Query 34 ( marks)

(a)  For (q_1):

(W = qE occasions s = qfrac{V}{d} occasions  frac{d}{2} = frac{qV}{2} )

For (q_2):

(W = qfrac{V}{second} occasions frac{3}{4}second = frac{3qV}{4} )

Therefore the work is larger for (q_2).

(b) The electrical discipline is (frac{V}{d}) for (q_1) in comparison with (frac{V}{second}) for (q_2) so the power (F = qE) on (q_1) could be stronger, and its acceleration upwards could be bigger.

It additionally has a shorter distance to journey to achieve plate (Y), so its time of flight and vary will likely be shorter in comparison with (q_2).