XII-Physics Karachi Board


Q.1 (A). Choose the correct answer from the given options.
i. RMS velocity of a gas molecule at absolute zero temperature is
9 x 10(6)m/sec
3 x 10(3)m/sec
ii. The heat required to produce a unit change in the temperature of a substance is called
Heat Capacity
Molar Heat
Specific Heat
Latent Heat
iii. The value of Baltzman's constant is
3.85 x 10(-23) Jk-1
2.185 x 10(-12) Jk-1
1.62 x 10-22 JK-1
1.38 x 10-23 JK-1
Q.1 (B). State the basic assumptions of the Kinetic Molecular Theory of Gases.
State the Gas Laws. How are they combined to give the equation of an ideal gas.
Define Co-efficient of linear expansion and Co-efficient of volume expansion and prove that the co-efficient of cuibal expansion is three times of the co-efficient of linear expansion. (β = 3α).
Show that the pressure of ideal gas is P = 1/3 pV2. Where p is the density of the gas. Verify Boyle's Law and Charle's Law on the basis of kinetic molecular theory.
Q.1 (C). Using the equation for pressure P = 1/3 pV2. Prove that the absolute temperature of an ideal gas is proportional to the average Kinetic Energy (K.E) of the molecules.
Q.1 (D). Find the root mean square velocity of hydrogen gas molecule at 100°C. Take the mass of hydrogen molecule 3.32 x 10(-27) Kg and K = 1.38 x 10-23 J/K.
Calculate the volume occupied by a gram mole of a gas at 10°C and pressure one atmosphere. (Given R = 8.313 J mol-1 K-1, 1 atmosphere = 1.01 x 10(5) N/m2)
Q.2 (A). Choose the correct answer for each from the given options.
i. The area of a carnot cycle represents.
Energy loss due to leakage
Heat rejected
Heat absorbed
Useful work
ii. 273 K is equal to
iii. Two ends "A" and "B" of a rod are at temperature -10°F and -30°F. The heat will flow from
-30°F to -10°F
-10°F to -30°F
Will not flow to all
None of the above
Q.2 (B). Define Thermal expansion and Thermodynamics. State the First law of Thermodynamics. Describe Isobaric process, Adiabatic Process, Isochoric Process and Isothermal Process with their graphical representation.
What is Thermodynamics? Give two statements of the Second Law of Thermodynamics and prove that both the statements of the Second Law of Thermodynamics and prove that both the statements are identical and equivalent.
Q.2 (C). Describe the construction and working of a Carnot's Engine. Derive an expression for the efficiency of Carnot's Engine. Draw labeled graphical representation of the Carnot's Engine to explain its complete operation.
Explain the concept of Entropy. Also state the Second Law of Thermodynamics in terms of Entropy?
Q.2 (D). A heat engine are works 1000 Joules at the same time rejects 4000 Joules of heat energy to the cold reservoir. What is the efficiency of the heat engine? If the difference of temperature between sink and source of this engine is 75°C. Find the temperature of its source.
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Q.3 (A). Select the correct answer for each from the given options.
i. The minimum electrical charge possible in isolated form is
1.6 x 10(-19)C
1 x 10(12)C
1 x 10(-6)C
One Coulomb
ii. The change of Potential Energy of a unit charge between two points in an electrical filed is called
Potential Difference
iii. The direction of induced current is given by
Ampere's Law
Faraday's Law
Lenz's Law
Snell's Law
Q.3 (B). State Coulomb's Law and give its mathematical relation for the force between the charges when placed.
In a free space
In a medium of relative permitivity (Єr)
Define Resistance and write down its units? How does the resistance of a conductor depend upon temperature? Derive the equation for the resistance at a given temperature.
Define Electric Potential. Derive the relation between an Electric Field and Potential Difference.
Define the Capacity of a Capacitor. Derive an expression for the Capacitance of a parallel plate capacitor having some dielectric between its plates.
Derive a relation the equivalent capacitance of the three capacitors connected in parallel or series.
Q.3 (C). Describe a method for determining the ratio of charge and mass of an electron. Derive the mathematical equation. Explain J.J Thomson method to find charge to mass (e/m) ratio of an electron.
Q.3 (D). How many excess electrons must be placed on each of the two small spheres placed 3.0 cm apart if the force of repulsion between them is 10-19 N.
Q.4 (A). Choose the correct answer for each from the given options.
i. When a resistor carries a current "I", the power dissipated by it is "P" If the same resistor has the current of 31, the power dissipated will be.
None of the above
ii. Coulomb/Volt is the unit of
iii. Decreasing the separation of two positive charges by one-half will cause the force of repulsion to be charged by
1/4 times
2 times
1/2 times
4 times
Q.4 (B). Define Electromagnetic Induction and Induced e.m.f. State Faraday's Laws of electromagnetic induction. Also state Lenz's law for induced e.m.f.
Define Self Deduction and Self-Inductance and obtain an expression for the Self of Mutal Induction and obtain an expression for the Mutual Inductance of two coils.
What is motional e.m.f. Derive an expression for it.
Q.4 (C). State the law which governs the Potential difference across the conductor related to its dimensions? Derive the formula for the temperature co-efficient of resistivity.
Q.4 (D). An aeroplane is flying in a region where the vertical component of hte earth's magnetic filed is 3.2 x 10(-4) Tesla. If the wing wing span of the aeroplane is 50 meters and its velocity is 360 Km/hour find the Induced E.M.F between the tips of the wings of the aeroplane.
Q.5 (A).Select the correct answer for each from the given options.
i. The semi conductor diode is used as
ii. The maximum resistance in an A.C Circuit is offered by
Electric bulb
iii. The path of the neutron moving normal to a magnetic field is a/an
Straight line
Q.5 (B). What is galvanometer? With the help of neat and labeled diagram, describe the construction and working of a moving coil galvanometer. Describe how a galvanometer can be converted into an Ammeter and a Voltmeter, derive mathematical relation for each of them.
What is Transistor? Describe the working of a NPN and PNP transistor.
Q.5 (C). What is a diode? How can a diode be used as a rectifier?
Explain with diagrams the forward and reverse biasing of a p-n junction.
What is doping? How p-type and n-type semi conductors are made?
Q.5 (D). A maximum 50 milliamperes current be allowed to flow through 19.8 ohm coil of a galvanometer. Calculate the length of a Copper is to be used as a shunt. The diameter of the wire is 4mm, the specific resistance (ρ) of copper is 1.6 x 10(-8) ohm-m.
Q.6 (A). Select the correct answer for each from the given options.
i. The quantity ΔV/ΔS is called
Electrical Potential
Electric field intensity
Potential gradient
Electric induction
ii. In a wheat stone Bridge circuit we balance
All of these
iii. The unit of least count on a galvanometer represents
Q.6 (B). State Ampere's Circuit Law. Derive an expression for the magnetic induction inside a current carrying long solenoid with the help of Ampere Law's. Draw also neat diagram.
Define Torque. Derive the equation for the couple of torque acting on a current carrying rectangular coil suspended in a uniform magnetic field.
With the help of neat and labeled diagram describe the construction and working of an Electric Motor.
Q.6 (C). Explain Electric Flux. Under what condition will the flux through the surface be.
Q.6 (D). A coil of 50 turns is wound on an ivory frame 3 cm x 6 cm which rotates in a magnetic filed B = 2 web/m2 what will be the torque acting on it, if a current of 5 amperes passes through it and the plane of the coil makes an angle of 45°C with the field.

Q.7 (A). Select the correct answer for each from the given options.
i. If a small quantity of radioactive iodine 131/53I is taken in food, most of it deposited in
Thyroid glands
All glands
ii. The process of Β-particle emission from a nucleus involves the change in
Mass number
Mass and charge number
Charge number
No charge occurs
iii. The reverse of pair production is known as
Annihilation of electron and positron
Annihilation of electron and proton
Q.7 (B). State Bohr's Postulates for a hydrogen atom. Derive the expression for the total energy of the electron in the orbit of the hydrogen atom.
What are Black body and Black Body Radiation? State the laws governing the Black Body Radiation. Give their mathematical expressions.
Define the term Radioactivity and Half life of Radioactive Element. Describe the changes Produced in the nucleus as a result of α, Β, γ emissions. State and explain the laws of Radioactivity Decay with its exponential curve.
Q.7 (C). What are the postulates of the Special Theory of Relativity? Explain any three results of Einsteins Theory of Relativity.
What do you understand by the Frame of Reference and Inertial Frame of Reference? Give one example of each from daily life. Briefly describe the three basic equations from relativity predicting the relativistic changes.
Define Work Function, Stopping Potential and Threshold frequency.
Q.7 (D). In a hydrogen atom an electron experiences transition from a state whose binding energy is 0.54ev to the state whose energy is 10.2ev (RH = 1.097 x 10(7) m-1) Calculate
The quantum numbers of the two states
The wavelength of the photon emitted
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Q.8 (A). Select the correct answer for each from the given options.
i. The disintegration of a photon into electron and position near a heavy nucleus is known as
β - decay
α - decay
Pair Production
ii. Write the True or False for the following
The track formed in Wilson Cloud Chamber due to gamma (γ) rays is a thick and continuous line.
iii. Fill in the blanks with the correct answer
The ratio of the mass of proton to the mass of electron is ____________.
Q.8 (B). Explain the phenomenon of Compton Effect and obtain an expression for the increase in the wavelength of the scattered photon.
Explain the Fission Reaction with the help of nuclear process that a neutron can disintegrate into an electron and a photon. Write down the conversion equations in support of your answer. Explain Chain Reaction in (92U135).
Q.8 (C). What do you understand by term LASER? Describe the construction and working of Ruby Laser. Describe the principle of Laser.
Define Annihilation of matter. What do you understand by pair Production? Describe the condition for pair production with the help of an equation.
State and explain Heisenberg's Uncertainty Principle and derive the relative mathematical expression.
Describe de Broglie Hypothesis for the discription of wave nature of particles.
Describe the production of x-rays. Also give the characteristics and uses of x-rays.
Describe the construction and working of Geiger Counter.
Q.8 (D). In Compton scattering process the fractional change in wavelength of x-rays photon is 1% at an angle 120° (θ = 120°); find the wavelength of x-rays used in this experiment.

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