Sub. code 1021
NEB — GRADE XII
2078
Old Question
Class 12 Physics Old Question 2078
The candidates are required to give their answers in their own words as far as practicable. The figures in the margin indicate full marks.
Pass Marks : 32
सबै प्रश्नको उत्तर दिनुहोस् । (Attempt All Questions)
This old question paper is for Class 12 Physics, 2078 (subject code 1021), carrying full marks of 75 with a pass mark of 32, to be completed within 3 Hours. Model answers are available for questions that have one — reveal them with a free account (a few reveals) or a paid plan (unlimited).
Group A
Rewrite the correct answer in your answer sheet
Which of the following is a correct formula for calculating the radius of gyration of a rotating object?
A horizontal stream of air is blown under one of the pans of a beam balance as shown in the figure. What will be the effect of this on the pan?
goes up
goes down
remains unaffected
rotates
What will be the height of a capillary on the surface of the Moon if it is on Earth?
$h$
$\frac{h}{6}$
zero
What is the coefficient of performance of an ideal refrigerator working between ice point and room temperature ?
$0$
$1$
$10$
A thermodynamic system is taken from to via and then returned to via as shown in the diagram. The area of which segment of the graph represents the total work done by the system?
$P_1 A C B P_2 P_1$
$ACBB'A'A$
Which one of the following directly affects the quality of sound?
shape of the source
frequency
intensity
wave form
A diffraction pattern is obtained using a beam of red light. What will be the effect on the diffraction pattern if the red light is replaced with white light?
All bright fringes become white.
All bright fringes, except the central one, become white.
All bright fringes become colourful.
All bright fringes, except the central one, become colourful.
A circular coil has turns, radius , and carries a current . Which physical quantity is given by the product ?
magnetic flux
magnetic flux density
magnetic moment
electric field intensity
A coil having turns and cross-section area carries current . Which physical quantity does the product represent?
magnetic flux of the coil
magnetic flux density of the coil
magnetic moment of the coil
magnetic susceptibility of the coil
What happens to the neutral temperature if the cold junction of a thermocouple is decreased?
increases
decreases
remains the same
approaches inversion temperature
What is the point where the seismic waves start called?
epicentre
hypocentre
metacentre
seismic centre
Group B
Short Answer Question
Define “surface tension”.
Establish a relation between surface tension and surface energy of a liquid.
Two spherical raindrops of equal size are falling vertically through the air with a certain terminal velocity. If these two drops were to coalesce to form a single drop and fall with a new terminal velocity, explain how the terminal velocity of the new drop compares to the original terminal velocity
Angular speed of a rotating body is inversely proportional to its moment of inertia
Define “moment of inertia‟
Explain why angular velocity of the Earth increases when it comes closer to the Sun in its orbit.
If the Earth were to shrink suddenly, what would happen to the length of the day? Give reason.
State Bernoulli principle.
Derive Bernoulli‟s equation
You can squirt water from a garden hose a considerably greater distance by partially covering the opening with your thumb. Explain how this works.
Define “harmonics‟ in music
Calculate the frequency of a monotonous sound produced by a 30 cm long flute open at both ends and being played in the first harmonic. [Velocity of sound in air= 330 ms-1]
The flute mentioned in the question (ii) was being played by a passenger on a stationary bus. The bus then moves uniformly. Explain what change in the pitch of the flute sound, if any, a person sitting on a bench at the bus park will feel when the bus starts moving.
State the second law of thermodynamics.
A refrigerator transfers heat from a cold body to hot body. Does this not violate the second law of thermodynamics? Give reason.
In the given figure, a heat engine absorbs Q amount of heat from a source at temperature T and rejects Q amount of heat to a sink at temperature T doing some external work W.
Obtain an expression for the efficiency of this heat engine
Under what condition does the efficiency of such engine become zero percentage, if at all?
A student wants to measure the magnetic flux density between the poles of two weak bar magnets mounted on a steel yoke as shown in the figure. The magnitude of the flux density is between 0.02T and 0.04T.
Define Magnetic flux density.
One way of measuring the magnetic flux density could be the use of a Hall probe. Suggest one reason why Hall probe is not a suitable instrument to measure the magnetic flux density for the arrangement shown in the below figure.
State Law of electromagnetic induction
Explain the significance of the negative sign
State what the symbols ε and dϕ/dt represent in the equation.
Two identical copper balls are dropped from the same height as shown in the figure. Ball P passes through a region of uniform horizontal magnetic filed of flux density B. Explain why ball P takes longer than ball Q to reach the ground.
Ultraviolet radiation of frequency is incident on the surface of an aluminium plate whose work function is
Show that the maximum speed of the electrons emitted from the surface of the aluminium is $8.6 \times 10^{5}\,\text{m s}^{-1}$
State and explain what change, if any, occurs to the maximum speed of the emitted electrons when the intensity of the ultraviolet radiation is increased.
State Bohr’s postulates of the atomic model.
The figure shows the Lyman series of energy transmission in the hydrogen atom. Calculate the frequency of a photon emitted by an electron jumping from the second excited state to the ground level.
Sketch the symbol of a p-n junction diode and indicate the polarity of its ends.
Copy the outline of a diode bridge rectifier and complete it by adding diodes in the gaps.
Group C
Long Answer Question
Prove that this force will make the rock vibrate with simple harmonic motion.
Show that the speed of an object undergoing simple harmonic motion is given by the expression
where the symbols carry standard meanings.
Calculate the maximum speed of a building shaken by S-waves of 21Hz and amplitude 0.05m.
Explain why tall buildings are more susceptible to damage by S-waves which generally have a low frequency.
A student sets up a circuit as shown in the figure given below to measure the emf of a test cell.
Explain why he is unable to find a balance point and state the change he must make in order to achieve the balance
State how he would recognize the balance point.
He obtained the balance point for distance 37.5cm using a standard cell of emf 1.50V. And for the test cell, the balance distance AB was 25.0 cm. Calculate the emf of the test cell.
He could have used an ordinary voltmeter to measure the emf of the test cell directly. The student, however, argues that the above instrument is more precise than an ordinary voltmeter. Justify his logic.
Explain what is meant by quantization of charge.
In a Millikan‟s oil drop experiment, an oil drop of weight 1.5 x 10 N is held stationary between plates 10mm apart by applying a p.d. of 470V between the plates.
State the condition necessary for the drop to remain stationary. Also, sketch the forces acting on the oil drop.
Calculate the charge on the oil drop.
Derive an expression for a radioactive process where the symbols carry their standard meanings.
A student measured the activity of a sample of radioactive rock. Her results are presented in the graph.
Explain why the data are scattered.
Determine the half-life of the sample
Paper Overview & Analysis
2078
Year
Old Question
Type
75
Full Marks
32
Pass Marks
3 Hours
Duration
53
Question Items
Question Type Breakdown
Group Breakdown
Chapter Breakdown
| Fluid statics | 8 items | 12 marks |
| Acoustic phenomena | 3 items | 4 marks |
| First law of thermodynamics | 2 items | 2 marks |
| Magnetic Field | 2 items | 2 marks |
| Rotational Dynamics | 1 item | 1 mark |
| Diffraction | 1 item | 1 mark |
| Thermoelectric Effects | 1 item | 1 mark |
| Wave motion | 1 item | 1 mark |
| Waves in pipes and strings | 1 item | 2 marks |
| Electrons | 1 item | 3 marks |
| Quantization of Energy | 1 item | 2 marks |
Chapter breakdown covers 22 of 53 question items on this paper — the rest aren't tagged to a chapter yet.