**11**. A block and tackle pulley arrangement has 6 pulleys in which an effort of 50N supports a load of 200N, calculate the efficiency of the machine

**A.**80.0%**B.**76.6%**C.**66.7%**D.**60.7%

**Correct Option: Answer is C**

Efficiency = \(\frac{ma}{V.R}\) x \(\frac{100}{1}\)

V.R = number of pulleys = 6

ma = \(\frac{\text{Load}}{\text{Effort}}\) = \(\frac{200}{50}\) = 4

Effiecieny = \(\frac{4}{6}\) × 100 = 66.67%

**12. **Three 3ω resistance are connected in parallel what is the equivalent resistance?

**A.**1ω**B.**9ω**C.**3ω**D.**0.33ω

**Correct Option: Answer is A**

Resistor connected in a parallel have an equivalence given by

\(\frac{1}{\text{Reff}}\) = \(\frac{1}{3}\) + \(\frac{1}{3}\) + \(\frac{1}{3}\)

= \(\frac{1 + 1 + 1}{3}\) = \(\frac{3}{3}\) = 1

Reff = 1ω

**13. **Which of the following instruments helps to maintain the correct humidity and temperature of a building?

**A.**A compressor**B.**A refrigerator**C.**Air blower**D.**Air conditioner

**Correct Option: Answer is D**

Compressor is an instrument to supply air or other gas at increased pressure

Refrigerator is an appliance to keep things cold

Air blower is used to release air

Air conditioner is used to remove heat and maintain a stable temperature in an occupied space

**14. **The thermal expansion of a solid is an advantage in

**A.**Balance wheel of a watch**B.**Construction of steel rail lines**C.**Construction of large steel bridges**D.**Fitting of tyres on wheels

**Correct Option: Answer is A**

Thermal expansion of a solid is majorly advantageous in the use of bimetallic strip in the balance of a watch so as not to lose time

**15. **The S.I unit of moment of a force is

**A.**kgm**B.**µm**C.**Jm**D.**µm−1

**Correct Option: Answer is B**

Moment of a force is the product of a force and the perpendicular distance from the line of action of the force

Moment = force × distance

= N × m

= Nm

**16. **A block and tackle pulley arrangement has 6 pulleys in which an effort of 50N supports a load of 200N, calculate the efficiency of the machine

**A.**80.0%**B.**76.6%**C.**66.7%**D.**60.7%

**Correct Option: Answer is C**

**17. **Calculate the light of the image formed by a pinhole camera of length 12cm used to photograph an object 60cm away from the hole and 70cm high

**A.**10 cm**B.**16 cm**C.**5 cm**D.**14 cm

**Correct Option: Answer is D**

Magnification = \(\frac{\text{Length of camera}}{\text{distance of object from pin hole}}\)

m = \(\frac{12}{60}\)

= 0.2

Also magnification m = \(\frac{\text{Height of image}}{\text{Height of object}}\)

∴ Height of image = m × height of object

= 0.2 × 70

= 14cm

**18. **When two objects P and Q are supplied with the same quantity of heat, the temperature change in P is observed to be twice that of Q. The mass of P is half that of Q. The ratio of the specific heat capacity pf P to Q is

**A.**1:4**B.**4:1**C.**1:1**D.**2:1

**Correct Option: Answer is C**

H = mcθ

H_{P} = H_{Q}, θ_{P} = 2θ,

m_{P} = \(\frac{1}{2}\)m_{Q}

∴ H_{P} = m_{Q}C_{P}θ_{P}, also HQ = m_{Q}C_{Q}θ_{Q}

Since H_{P} = H_{Q}

∴ m_{P}c_{P}θ_{P} = m_{Q}c_{P}θ_{q}

Putting in the conditions

\(\frac{1}{2}\)m_{Q} × c_{P} × 2θ_{Q} = m_{Q} × θ_{Q} × c_{Q}

∴ c_{P} = c_{Q}

\(\frac{C_p}{C_Q}\)= \(\frac{1}{1}\)

= 1:1

**19. **When the r.m.s value of a source of electricity supply is given as 240v, it means that the peak value of the supply is

**A.**240v**B.**340v**C.**480v**D.**57600v

**Correct Option: Answer is B**

The relationship between the peak value and r.m.s value of electricity supply is given as

V\(_{r.m.s}\) = \(\frac{V_o}{\sqrt{2}}\)

where V_{o} = peak voltage

∴ V_{o} = V\(_{r.m.s}\) × √2

= 240 × √2

= 339.5v

= 340v

**20. **Which of the following operations can be used to convert an alternative current dynamo into a direct current dynamo

**A.**number of turns in the coil is increased**B.**strength of the field magnet is increased**C.**slip rings are replaced with split ring cummutator**D.**coil is wound on a soft iron armature

**Correct Option: Answer is C**

A d.c generator is one in which its current is allowed to flow in one direction even through it may vary in value an a.c generator can only be made to produce a d.c by replacing the two slip rings with a single split ring or commutator.