Physics XII Karachi Board Numericals

Section A

1. Find the efficiency of a carnot engine working between 100°C and 50°C.

2. Find the root mean square of a hydrogen molecle at 7°C. Take the mass of a hydrogen molecule to be 3.32 x 10-27 kgm and Boltzmann’s constant = 1.38 x 10-23 joules/°K.

3. 540 calories of heat is required to vapoirze 1 gm of water at 100°C. Define the entropy change involved in vaporizing 5gm of water. (1 calorie = 4.2 joules)

4. A glass flask is filled to the mark with 60cm3 of mercury at 20°C. If the flask and its contents are heated to 40°C, how much mercury will be above the mark? a for glass = 9 x 10-6 /°C and b for mercury = 182 x 10-6 /°C.

5. A carnot engine whose low temperature reservoir is 200°K has an efficiency of 50%. It is desired to increase this to 75%. By how many degrees must the temperature be decreased, if higher temperature of the reservoir remains constant?

6. In an isobaric process, when 2000J of heat energy is supplied to a gas in a cylinder, the piston moves through 0.1m under a constant pressure of 2 x 1.01 x 105 N/m2. If the area of the piston is 5 x 10-2m2, calculate the work done and the increase in the internal energy of the system.

7. Find the root mean square velocity of the nitrogen molecules at 27°C. Given the mass of nitrogen molecule to be 4.67 x 10-26kg. K = 1.38 x 10-23 joule/K.

8. A meter bar of steel is correct at 0°C and another at –2.5°C. what will be the difference between their lengths at 30°C.

9. A heat engine performs work at the rate of 500KW. The efficiency of the engine is 30%, calculate the loss of heat per hour. (a = 12 x 10-5 /°K)

Section B

1. Two capacitors of 2.0 mF and 8.0 mF capacitance are connected in a potential difference of 220 volts is applied. Find the charge and the potential difference for each capacitor.

2. A 10 eV electron is moving in a circular orbit in a uniform magnetic field of strength 10-4 web/m2. Calculate the radius of the circular path. (Mass of electron -= 9.11 x 10-31 kg and charge of electron = 1.6 x 10-19C).

3. A transformer has 1000 turns in the primary coil. If the input voltage of the transformer is 200 volts. What should be the number of turns of the secondary coil to obtain an output of 6.0 volts?

4. Calculate the force of repulsion on +2 x 10-8 coulomb charge, if it is placed before a large vertical charged plate whose charge density is +20 x 10-4 colomb/m2. (Îo = 8.85 x 10-12 coul2/Nm2)

5. A solenoid 20cm long has three layers of windings of 300 turns each. If a current of 3 amperes is passed through it, find the value of the magnetic field of induction B. (mo = 4p x 10-7 web/amp.m)

6. A 500 turn coil in a A.C Generator having an area of 100 cm2 rotates in a magnetic field of value 50 tesla. In order to generate 220 volts maximum, how fast is the coil to be rotated? Express you answer in terms of the number of revolution per second.

7. A capacitor of 200pF is charged to a Potential difference of 100 volts. Its plates are then connected in parallel to another capacitor and is found that the potential between the plates falls to 60 volts. What is the capacitance of the second capacitor?

8. a particles are accelerated from rest at a potential difference of 1KV. They then enter a magnetic field B = 0.2 T perpendicular to their direction. Calculate the radius. Given mass m = 6.68 x 10-27kg, 1 = 2e, e = 1.6 x 10-19C)

9. A moving coil galvanometer has a resistance of 25W and it gives full-scale deflection for a potential difference of 50MV. If the galvanometer is to be converted into a voltmeter reading up to 50volts, what should be the resistance of the series resistor?

10. A thin sheet of positive charge attracts a light charged sphere having a charge –5 x 10-6C with a force 1.695N. If Îo= 8.85 x 10-12 C2/Nm2, calculate the surface density of the charge.

11. Two capacitors of capacitance 4.00 mF and 6.00 mF are charged to the potential difference of 300 volts and 400 volts respectively. They are then connected in parallel. What will be the resultant potential difference and charge on each capacitor?

12. A platinum wire of diameter 0.2 mm is sound to make the resistor of 40W. How long a wire is needed for this purpose?

13. An electron is moving along a circle of radius 1.8 x 10-6m. Calculate the speed of the electron on entering perpendicularly in a uniform magnetic field of 5 tesla. Given e = 1.6 x 10-6 C and m = 9.11 x 10-3kg. (P = 11 x 10-8Wm)

14. A galvanometer of resistance 60W gives full scale deflection with a current of 4mA. A resistance of 10940W is connected in series with the coil to convert it into voltmeter, find the range of voltmeter obtained.

Section C

1. The range of visible light is 4000A° to 7000A°. Will photoelectrons be emitted by a copper surface of work function 4.4 eV, when illuminated by visible light?

2. The energy of an electron in an excited hydrogen atom is –3.4eV. Calculate the angular momentum of the electron according to Bohr’s theory. (h = 6.63 x 10-34Jsec)

3. Find the wavelength of light which is capable of lionizing a hydrogen atom R = 1.097 x 107/m.