Assessment Quiz: Lesson 4: The Electric Transformer and Electric Motor (DC Motor)

Question 1

Why does an electric transformer fail to operate when connected to a 24 V DC accumulator battery?

Accepted Answer

The DC battery produces a constant magnetic flux with zero time rate of change

Answer

The accumulator voltage is too high

Answer

Soft iron does not conduct magnetic flux with DC

Answer

Direct current causes immediate short circuiting

Question 2

The hydrostatic pressure exerted by a static homogeneous liquid of density rho at depth h beneath its free surface is expressed by:

Accepted Answer

P = rho * g * h

Answer

P = rho * h / g

Answer

P = 1/2 rho * g * h^2

Answer

P = rho * g / h

Question 3

A diver descends to a depth of 30 meters in seawater (density = 1030 kg/m^3). If atmospheric pressure is 1.013 x 10^5 Pa and g = 9.8 m/s^2, the total absolute pressure experienced by the diver is approximately:

Accepted Answer

4.04 x 10^5 Pa (approx. 4.0 atmospheres)

Answer

3.03 x 10^5 Pa

Answer

1.01 x 10^5 Pa

Answer

6.06 x 10^5 Pa

Question 4

Pascal's principle states that when pressure is applied to an enclosed, incompressible fluid, it is transmitted:

Accepted Answer

Undiminished to every portion of the fluid and to the walls of the containing vessel

Answer

Only downwards towards the bottom of the vessel

Answer

With an exponential decay as distance increases

Answer

Strictly to compressible gases

Question 5

In a hydraulic press, the ratio of the cross-sectional area of the large piston to that of the small piston is 50. If a force of 100 N is exerted on the small piston, the maximum force exerted by the large piston is:

Accepted Answer

5000 N

Answer

2 N

Answer

2500 N

Answer

50,000 N

Question 6

The mechanical advantage (eta) of an ideal hydraulic press equals all of the following ratios EXCEPT:

Accepted Answer

Work done by the large piston / Work done on the small piston > 1

Answer

Force on the large piston / Force on the small piston (F / f)

Answer

Area of the large piston / Area of the small piston (A / a)

Answer

Distance moved by the small piston / Distance moved by the large piston (y1 / y2)

Question 7

The relative density (specific gravity) of a substance is defined as:

Accepted Answer

The ratio of the density of the substance to the density of pure water at 4°C

Answer

The mass of the substance divided by its volume at 100°C

Answer

The product of density and the acceleration due to gravity

Answer

The reciprocal of the buoyant force

Question 8

In a U-tube manometer containing two immiscible liquids in equilibrium, the heights of the liquid columns measured above the separating surface are:

Accepted Answer

Inversely proportional to their respective densities (h1 / h2 = rho2 / rho1)

Answer

Directly proportional to their densities

Answer

Equal regardless of the liquids used

Answer

Proportional to the square of the cross-sectional area of the tube

Question 9

Why are hydroelectric storage dams constructed with a base that is significantly thicker than the crest?

Accepted Answer

Because hydrostatic water pressure increases linearly with depth (P = rho * g * h), exerting immense overturning forces at the bottom

Answer

To prevent solar radiation from penetrating the foundation

Answer

To reduce the gravitational pull of the bedrock

Answer

To allow fish to swim upstream through drainage gates

Question 10

A metallic cube of side length 10 cm and density 7800 kg/m^3 is completely submerged in water (density 1000 kg/m^3). The buoyant force (upthrust) acting on the cube is (g = 10 m/s^2):

Accepted Answer

10 N

Answer

78 N

Answer

68 N

Answer

100 N

Comparison: generator and motor

10 Comparison: generator and motor

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