AKUEB Pre-board exams, Solution of Physics (Paper II)
Aga Khan Education services Pakistan
Pre Board Examinations (AKUEB) March, 2023
Grade XII
Physics Paper II
Solved by: Sadiq
Saleem Lecturer Physics
Station: AKHSS Gahkuch Posted at: Physicsgossips.blogspot.com
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Q1. If a point charge
‘q’ of mass ‘m’ is released in a non-uniform electric field with a field line
pointing in the same direction. Will it make a rectilinear motion? Justify your
answer with regards to electrostatic force.
Answer:
Yes, the point charge q will make a
rectilinear motion in the direction of the electric field lines. As the
electric field lines are always unidirectional and they are considered as a map
of electric field strength and hence they give information about the magnitude
of electrostatic force at different points around a source charge.
Q2. Consider the
connection of a voltmeter in an electric circuit.
a. State the reason for connecting a voltmeter
in parallel combination with a load
Voltmeter is connected in parallel with a load to measure the actual
potential drop across the load. If it is
connected in series then no current will be there in the circuit due to its
high resistance. Hence it is connected in parallel to the load across which
potential difference is to be measured.
b. Why the resistance of voltmeter
is kept very high?
A Voltmeter has very high resistance to ensure that it's
connection do not alter flow of current in the circuit.
c. How can a galvanometer be converted into
ammeter?
A
galvanometer can be converted into ammeter by adding a low resistance is
parallel with a galvanometer.
Q2. Does the
induced EMF in a circuit depends on the resistance of the circuit? Explain t
with regards to Faraday’s Law of EM induction.
Answer.
The mathematical expression of the induced emf according to
Faraday’s law of EM induction is:
From
this expression, it is clear that the induced emf does not depend on the
resistance of the circuit, but it depends on the number of turns of the coil
and rate of change of magnetic flux through it. However, the induced current
depends on the resistance of the coil.
Q4. Name and mention
the uses of any two EM waves in our daily life
Answer:
Uses of EM waves:
a.
Radio waves are used in communication and
internet.
b.
X-rays are used in making images of the internal
of human body
Q5.
Describe the formation of the following magnetic substances.
a. Paramagnetic materials have some unpaired electrons due to these unpaired electrons the net
magnetic moment of all electrons in an atom is not added up to zero. Hence
atomic dipole exists in this case. Paramagnetic materials are feebly magnetized
in the direction of the magnetizing field.
b. In diamagnetic materials, there are no atomic dipoles due to the pairing between the electrons.
When an external magnetic field is applied, dipoles are induced in the
diamagnetic materials in such a way that induced dipoles opposes the external
magnetic field according to Lenz’s law.
Q6. How does
the electrons move across the two junction in a NPN transistor?
Answer:
In NPN transistor, the emitter base junction is forward biased and
the base-collector junction is connected in reverse bias. The electrons from
the emitter (N-region) will move into base (P-region) having very small
thickness, few of the electrons will move towards the positive terminal of
battery through base but most of electron enters into the collector N-region
has larger thickness and it is also reverse biased.
Q7. Why does
the gaseous substance exhibit a line spectrum? Whereas a liquid or a solid
substance exhibits a continuous spectrum?
Answer:
The gaseous substances exhibit line spectrum because their atoms
absorb the light of specific wavelength and give off the same light when their
atoms de-excite.
Contrary to this, liquids and solids absorb the light of wide
range of wavelengths, hence they give the continuous spectrum.
Q8. Whenever
any particle is emitted out of any radioactive element. It is accompanied by
some changes in the nucleus of the element. Explain the formation of a daughter
element ‘Y’ from its parent element ‘X’ as a result of α, β, and γ emissions
Answer:
Whenever an excited atom decays:
a.
By
emitting α-radiations, the proton number or atomic number Z of the
parent nuclide reduces by 2 and its mass number or nucleon number A decreases
by 4.
b.
By emitting β-radiations, the parent
nuclide has its proton number Z increased by 1 but its mass number or nucleon
number A remains unchanged.
c.
By emitting γ-radiations, the atomic number
and mass number number of the parent nuclide does not change because γ-radiations
are beam of photons having no charge and mass.
Q9.
Consider two arrangements of N identical resistors,
one in parallel and the other in series. Each of these arrangements are connected
to batteries of the same voltage. Calculate
i.
The
equivalent resistance in each arrangement
ii.
The ratio of
power dissipated in parallel to the power dissipated in series.
Answer.
Let we have two resistors in series and in parallel combination.
So
N=2
Q10. Consider
the surfaces of a yellow star, an orange star and that of a red star. In the
light of blackbody radiation, explain
i.
Which surface
has the highest temperature?
ii.
Which surface
has the lowest temperature?
Answer:
B. Suppose ‘speedo’
one of the 20 year old twins takes off in a spaceship travelling at very high
speed to a distant star and back again, while ‘Gaslo’ the other twin remain on
earth. According to Gaslo, speedo will age less.
i. Name the
theory whose consequence would explain the above phenomenon.
Ans: Special
Theory of Relativity explains the above phenomenon.
ii.. Name the
phenomenon that is taking place
Ans: The phenomenon taking place is the
phenomenon of Time dilation.
iii.
Explain
the phenomenon by taking the relativistic effect into consideration and
supporting it with a mathematical expression.
Ans.
Q11. A 35 volt source is connected to a series
circuit of 600 ohm and R. If a voltmeter of internal resistance 1.2K ohm is
connected across a 600 ohm resistor and it reads 5V, find the value of R by
drawing a circuit diagram.
Answer.
Q10 (b).
Describe the
characteristics of a photoelectric effect in SIX points.
Answer: Characteristics
of Photoelectric effect:
1.
The energy of incident light is responsible
for the emission of photoelectrons
2.
The emitted electrons carry different
energies, the maximum energy of the photoelectrons depends upon the particular
metal surface and intensity of light.
3.
A minimum frequency is required for the
emission of the photoelectrons, below which no electrons will emit from the
metal surface.
4.
The magnitude of photocurrent depends on the
intensity of incident light.
5.
A part of energy carried by the incident
photon is used by electron to break away from the metal
6.
The K.E of the emitted electrons is directly
proportional to frequency of the incident light.
Q12.
a. Differentiate between volt and electron volt
by writing any three differences.
Answer:
|
Electron
volt refers to the energy carried by a moving electron |
Volt refers
to the potential difference between two points. |
|
Unit of
electron volt is Joules |
Volt
itself is a unit of potential difference |
|
The energy is associated with the particle you
place into that field |
Electric potential is a property associated
with the field in the space |
b. How the eddy current produced in the in core
of a transformer can be minimized? Explain the lamination process in three
points.
Answer:
The eddy current in the core of a
transformer can be minimized by a technique called lamination of the core.
Process of Lamination:
1. Many thin
sheets of a metal are pressed together
2. Thin insulating
layers are placed between the sheets
3. This limits
the circulation of eddy currents to the thickness of one sheet, rather than the
whole core.
c.
Mention any
three differences between N-Type and P-type semiconductors.
Answer:
N type semiconductors:
1.
They have free electrons in majority
2.
They can be formed by doping of group 5 elements with a
semiconductor Germanium or Silicon.
3.
They have high conductivity because of majority free electrons
P type
Semiconductors:
1.
They have positive holes in majority
2.
They can be formed by doping of group 4 elements with a
semiconductor Germanium or Silicon.
3.
They have less conductivity than N type semiconductors because the
mobility of holes is lower than electrons.
Thank you
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