SAHIWAL BOARD 2013
PAPER PHYSICS
PART-II
Time: 20 Min.
(Objective Part)
Marks: 17
Note: Four answer are given against each question in columns A,B,C and D. Select the right answer and on the separate Answer Sheet, fill the circle A,B,C or D with pen or marker in front of that question number.

• When an insulating medium is placed between two charges, the electrostatic force is.

(a) Increased
(b) Zero
(c) Decreased
(d) Same

• An inkjet printer uses_________ in its operation.

(a) Positrons
(b) Neutrons
(c) An electric charge
(d) Photons

• In gases the charge carriers are.

(a) Free electrons
(b) Holes
(c) Protons
(d) Electrons and ions

• One weber is equal to.

(a) NmA^-1
(b) Nm^-1 A
(c) NA/m
(d) NAm²

• If a charge is free to move in an electric field, then acceleration will be.

(a) qE/m
(b) qEm
(c) q/Em
(d) m/ qE

• In equation E = —VBL sin , is angle between.

(a) i and fi
(b) Y and I³
(c) P and L
(d) Land B

• Energy stored per unit volume is called.

(a) Power density
(b) Surface charge density
(c) Energy density
(d) Induction energy

• If is the root mean square value of voltage then peak value of voltage is.

(a) ,ri v,„„
(b) 21%m,
(c)
(d)

• The phase at negative peak will be.

(a) IrA
(b)
(c) 31r
(d)

• How many crystal systems are there on the base of geometrical arrangement of the atoms.

(a) 3
(b) 5
(c) 4
(d) 7

• The p-n junction on forward biasing acts as.

(a) Capacitor
(b) High resistor
(c) Inductor
(d) Low resistor

• The characteristic curve of p-n junction is between.

(a) Voltage and current
(b) Voltage and time
(c) Current and time
(d) Power and current

• If an object moves with speed of light, its mass becomes.

(a) Zero
(b) Infinity
(c) Same
(d) Small

• When platinum wire is heated, it becomes at 500°C?

(a) White
(b) Green
(c) Yellow
(d) Dull red

• Blamer series lies in region.

(a) Visible
(b) Invisible
(c) Ultraviolet
(d) Infra red

• When a nucleus emits a — particle, its mass number drops by.

 (a) 1
(b) 2
(c) 4
(d) 6

• Radioactivity happens due to disintegration of.

(a) Nucleus
(b) Mass
(c) Electrons
(d) Protons

Time : 3:10 hours
(Subjective Part)
Marks: 83

Section II

2. Attempt any EIGHT short questions. (8x2=16)

• Define electric flux. Write its SI units?
• How can you identify that which plate of capacitro is positively charged?
• Do electrons tend to go to region of high potential or of low potential?
• A Particle carrying a charge of 2e falls through a potential difference of 3.0.V. calculate the energy acquired by it.
• Is it possible to orient a current loop in a uniform magnetic field such that the loop experiences no torque? Explain
• Briefly explain the function of filament, cathode, grid and plates in C.R.O.
• If a charge particle is moving in a straight line through some region of space, can you say that magnetic field in the region is zero?
• Define magnetic flux density. Give its unit?
• Why does a motor draw more current when it is overloaded?
• Show that e and have same units.
• Does the induced e.m.f always act to decrease the magnetic flux through a circuit?
• Write two similarities and two differences between motor and generator.

3. Attempt any EIGHT short questions. (8x2=16)

• Describe a circuit which will give a continuously varying potential?
• Is the filament resistance lower or higher in a 500 W, 220 V light bulbs than in a 100 W, 220 V.
• Differentiate between the conventional and non conventional current.
• What is the root mean square value of current? Explain.
• What is meant by A.M and F.M?
• How the reception of a particular radio station is selected on your radio set?
• Define modulus of elasticity. Show that the units of modulus of elasticity and stress are the same.
• What is amorphous solid?
• What is critical temperature? What is its value for lead?
• Make the circuit diagram of full wave rectification. Also give the path of conventional current in it.
• What is the net charge on a n-type or p-type substance?
• Why ordinary silicon diodes do not emit light?

4. Attempt any SIX short questions. (6x2=12)

• What is Compton Effect?
• If speed of light were infinite what would be the equations of special theory of relativity reduce to?
• As solid is heated and begins to glow, why does it first appear red?
• State any two postulates of Bohr's model of hydrogen atom.
• How can the spectrum of hydrogen contain so many lines when hydrogen contain one electron?
• What is fluorescence? (vii) What is half life?
• What are isotopes? What do they have common and what are their differences?
• Why are heavy nuclei unstable?

Section-III

Attempt any THREE quesiions. (8x3=24)

5. (a) Determine the electric power dissipated in a resistor carrying current. (5)
(b) The time constant of a series RC circuit is t = RC. Verify that an ohm rimes Farad is equivalent to second. (3)

6. (a) Derive an expression for force on a moving charge in magnetic field. (5)
(b) The current in a coil of 1000 turns is changed from 5 A to zero in 0.2 s. If an average emf of 50 V is induced during this interval, what is the self inductance of the coil? (3)

7. (a) Write a note on R.0 series circuit. Find an expression for the impedance and draw its diagram. (5)
(b) A wire 2.5 m long and cross-section area 10-5m2 is stretched 1.5 mm by a force of 100 N in the elastic region. Calculate (i) the strain (ii) Young's modulus. (3)

8. (a) What are two types of transistor? Discuss current flow in an-p-n transistor by suitable circuit diagram. (5)
(b) An electron is placed in a box about the size of an atom that is about 1.0 x10 What is the velocity of the electron? (3)

9. (a) Define and explain the nuclear fusion reaction. (5)
(b) Calculate the longest wavelength of radiations for the paschen series. (3)