16. A small amount of air is introduced into the vacuum above the mercury in a mercury barometer tube. The mercury level goes down because the air molecules

**A.**heat the mercury and make it expand**B.**increase the pressure above the mercury.**C.**cool the mercury and make it contract.**D.**decrease the pressure above the mercury

**Correct Option: Answer is B**

**17. **Calculate the quantity of heat needed to change the temperature of 60g of ice at 0 °C to 80 °C. [specific latent heat of fusion of ice= 3.36 x 10^{5}Jkg−1specific heat capacity of water 4.2 x 10^{3} J kg−1]

**A.**4.80 kJ**B.**20.16 kJ**C.**40.32 kJ**D.**22.17 kJ

**Correct Option: Answer is C**

Heat needed to change 60g (0.06kg) of ice at 0^{o}C to water at 0^{o}

= 0.06 x 3.36 x 105J

= 0.2016 x 105 J

Heat required to raise the temp. of 60g (0.06kg) of water from 0^{o}C to 80^{o}C

= 0.06 x 4.2 x 103 x (80.0)J

= 0.06 x 4.2 x 103 x 80

= 20.16 x 103

= 0.2016 x 105

Total heat needed = (0.2016 + 0.2016) 105J

= 0.4032 x 105 J

= 40.32KJ

**18. **The wire of a platinum resistance thermometer has d resistance of 3.5Ωat 0 °C and 10.52Ωat 100°C. Calculate the temperature of the wire when its resistance is 7.5Ω.

**A.**78 °C**B.**25^{o}C**C.**30^{o}C**D.**57^{o}C

**Correct Option: Answer is D**

**19. **A transverse pulse of frequency 9 Hz traves 4.5m in 0.6 s. Calculate the wavelength of the pulse.

**A.**3.33 m**B.**0.30 m**C.**0.83 m**D.**1.20 m

**Correct Option: Answer is C**

Wavelength =Velocity (V)/frequency (f)

velocity= distance/time

=4.6/0.6

=7.5/9.9 = 0.83m

**20. **In which of the following media is the speed of sound the least?

**A.**Air**B.**Brass**C.**Water**D.**Wood

**Correct Option: Answer is A**

**21. **Which of the following characteristics of waves can a ripple tank be used to demonstrate?

Reflection

II. Refraction

III. Diffraction

**A.**I, II and Ill**B.**ll and ll only**C.**l and lII only**D.**I and II only

**Correct Option: Answer is C**

**22. **Which of the following graphs gives the correct relationship between energy and mass when mass is converted to energy?

**A.**A**B.**B**C.**C**D.**D

**Correct Option: Answer is B**

**23. **An 800 kg car moving at 80 km hr^{−1 }collides with a 1200 kg car moving at 40 km hr^{−1}in the same direction. If the cars stick together, calculate their common velocity.

**A.**60 km hr^{−1}**B.**8 km hr^{−1}**C.**40 km hr^{−1}**D.**56 km hr^{−1}

**Correct Option: Answer is B**

From momentum conservation

(800 x 80) – (1200 x 40)

= (800 + 1200) V

= 64000 – 48000 = 2000V

16000 = 2000V

V = 16000/2000

= 8kmh^{−1}

The common velocity = 8kmhr^{−1}

**24. **The mass of a load is doubled while the force acting on it is halved. The resulting acceleration of the load is

**A.**quadrupled**B.**quartered**C.**halved**D.**doubled

**Correct Option: Answer is A**

**25. **The maximum and minimum thermometer reads the

**A.**the maximum temperature during the day and the minimum temperature at night at all times.**B.**the maximum temperature at night and minimum temperature during the day from the last reset**B.**the maximum temperature at night and minimum temperature during the day at all times**D.**the maximum temperature during the day and minimum temperature at night from the last reset

**Correct Option: Answer is B**

**26. **An a.c. the generator can be converted to a d.c. generator by replacing the

**A.**commutator with an armature**B.**armature with a commutator**C.**commutator with slip rings**D.**slip rings with a commutator

**Correct Option: Answer is D**

**27. **Which of the following statements is the correct reason for using soft iron in making the armature or an electric bell?

**A.**It is a diamagnetic material**B.**It loses its magnetism readily**C.**It is not easily magnetized**D.**It retains its magnetism for a long time

**Correct Option: Answer is B**

**28. **The diagram above illustrates a meter bridge circuit under balanced condition. Determine the value of x.

**A.**71.4 cm**B.**10.0 cm**C.**28.6 cm**D.**57.2 cm

**Correct Option: Answer is D**

Using wheatstone bridge principle;

2/x=2/(100−x)

2(100 – x) = 2 x x

200 = 2x+2xx+2x

200 = 4x

x = 200/4

= 50cm

~ 57.2cm

**29. **Which of the following devices is used for storing electric charges?

**A.**Transformer**B.**Ammeter**C.**Potentiometer**D.**Capacitor

**Correct Option: Answer is D**

**30. **An electron of mass 9.1 x 10^{−31}kg moves with a speed of 2.0 x 10^{6}ms−1round the nucleus of an atom in a Circular path of radius 6.1 x 10^{11} Determine the angular speed of the electron.

**A.**3.28 x 10^{16}rad s−1**B.**8.55 x 10^{3}rad s−1**C.**9.11 x 10^{13}rad s−1**D.**5.22 x 10^{15 }rad s−1

**Correct Option: Answer is A**

Angular speed of the electron (W)

w = Velocity/Radius=V/R

= 0×10^{6}/6.1×10^{11}

= 3.28 x 10^{16}rads−1