Your Answer : (Not Answered)

Correct Answer : A

The correct matching is (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i).

• Bismuth is the classic diamagnetic material, with a relative permeability slightly below 1: (a)-(iv).
• Aluminium is paramagnetic, slightly above 1: (b)-(iii).
• Iron is ferromagnetic: (c)-(ii).
• That leaves neodymium, whose neodymium-iron-boron alloys make the strongest permanent magnets, for the paper's 'supermagnetic': (d)-(i).

The first three pairs are standard, and only one option has all three. The other options put aluminium with diamagnetism or neodymium with ferromagnetism in place of iron.

Your Answer : (Not Answered)

Correct Answer : B

The diamagnetic element is copper.

Diamagnetic materials are weakly repelled by a magnetic field: their relative permeability is slightly less than one and their susceptibility small and negative. Copper, silver, gold, bismuth and water are typical examples.

Iron is ferromagnetic and strongly attracted. Aluminium and calcium are paramagnetic: they are weakly attracted, with a relative permeability slightly greater than one.

Your Answer : (Not Answered)

Correct Answer : D

Danger notices are covered by IE Rule 35.

Rule 35 of the Indian Electricity Rules, 1956 requires the owner of every installation of medium or higher voltage to fix a permanent danger notice, in Hindi or English and the local language, with the sign of skull and bones, on each support of an overhead line and at other places where live parts are accessible.

The neighbouring rules deal with other matters: Rule 42 with accidental charging of metal work, Rule 43 with protective equipment such as fire buckets and first-aid boxes, and Rule 45 with precautions to be adopted by consumers, owners and electrical contractors.

Your Answer : (Not Answered)

Correct Answer : C

A mixer-grinder with a universal motor gets its different speeds from tappings on the field winding. If the motor runs on only one speed, the likely cause is that part of the field winding, which carries the tappings, is burnt out, so the speed taps no longer work. Loose brushes would cause sparking and noise, overloading would slow or stall the mixer at every setting, and absence of an earth connection is a safety fault, not a speed fault. The answer is Partially burnt out field winding, option (C).

Your Answer : (Not Answered)

Correct Answer : A

The primary current of a single-phase transformer at full load is the rating in volt-amperes divided by the primary voltage.

\[ I_{1} = \frac{25000}{1500} = 16.66\ \mathrm{A} \]

So the primary current drawn is 16.66 A, option (A). The turns of 250 and 40 give a secondary voltage of 240 V, and the secondary current is 25000 / 240, about 104 A, which is not asked. The value 32.33 A is double the correct one, 10 A would need 2.5 kV and 0.06 A is a reciprocal.

Your Answer : (Not Answered)

Correct Answer : B

A bushing in a transformer is the insulated passage by which a winding terminal comes out through the grounded metal tank. Its purpose is to provide electrical isolation between the winding terminals and the grounded tank, so the high voltage does not flash over to the tank. It does not isolate the winding from the core inside the tank, which is the job of the insulation, and it is not meant for magnetic isolation. The answer is option (B).

Your Answer : (Not Answered)

Correct Answer : D

The relay in the diagram is a dry reed relay. A reed relay has two thin magnetic metal blades sealed in a small glass tube, which come together when a magnetic field is applied by a coil or a magnet. The picture shows the slim glass capsule with its two leads.

A thermal relay uses a bimetal strip heated by current, an electromechanical relay has a coil, an iron armature and contacts in an open frame, and a hybrid relay combines an electronic circuit with a mechanical relay. So the fourth option is the answer.

Your Answer : (Not Answered)

Correct Answer : C

A latching relay has a mechanism, magnetic or mechanical, that holds the contacts in the position they were last moved to, so they stay there even after the power is cut off. An impedance relay and a differential relay are protective relays that return to their rest position when the coil is not energised, and a reed relay also opens when the field is removed. The answer is Latching relay, option (C). Latching relays are used where a state must be held without power being applied all the time, as in lighting control and in some protection circuits.

Your Answer : (Not Answered)

Correct Answer : C

If a person is in contact with a live electrical supply, the first thing to do is to break the contact by turning off the power supply at once, because the current will keep flowing through the victim as long as the supply is on. Pushing the victim with the bare hand would pass the current to the rescuer, and calling the ambulance or informing neighbours may be done afterwards but would not stop the current. The answer is Break the contact by turning off the power supply, option (C).

Your Answer : (Not Answered)

Correct Answer : B

The impedance of a coil is the square root of the sum of the squares of the resistance and the reactance, since the two are at right angles in the impedance triangle.

\[ Z = \sqrt{R^{2} + X_{L}^{2}} \]

\[ Z = \sqrt{4^{2} + 50^{2}} = \sqrt{2516} \]

\[ Z \approx 50.16\ \Omega \]

So the impedance is about 50.15 ohms, option (B), which is only a little more than the reactance because the resistance is small. Values of 110.12, 25 and 33 ohms do not follow from the formula.

Your Answer : (Not Answered)

Correct Answer : D

The inductive reactance of a coil is 2 pi f L, where f is the frequency in hertz and L is the inductance in henry.

\[ X_{L} = 2\pi f L = 2\pi \times 1000 \times 0.05 \]

\[ X_{L} = 314.15\ \Omega \]

The reactance is therefore 314.15 ohms, option (D). The inductance of 50 mH is 0.05 H, and the value 3.14 ohms comes from using 0.0005 H, while 50 and 101 ohms do not follow from the formula.

Your Answer : (Not Answered)

Correct Answer : D

A geyser is a water heater, and its purpose is to keep the heat in the water. The space between the outer casing and the inner tank is therefore filled with a heat insulating material, such as glass wool, so that little heat is lost to the surroundings and the water stays hot. A material of high heat conduction would carry the heat away, and high electric conductivity and high magnetic permeability have no use in the filling. The answer is heat insulation, option (D).

Your Answer : (Not Answered)

Correct Answer : B

Lighting systems are classified by the share of the light sent downward and upward: direct lighting sends 90 to 100 percent downward, semi-direct sends 60 to 90 percent downward, general diffused sends about equal amounts both ways, semi-indirect sends 60 to 90 percent upward, and indirect sends 90 to 100 percent upward. A system with 30 percent downward and 70 percent upward is therefore semi-indirect, option (B). The quantity is the upward light output divided by the total, and 70 percent upward is between the semi-indirect limits of 60 and 90 percent.

Your Answer : (Not Answered)

Correct Answer : A

Luminous efficiency is the light output in lumens divided by the electrical power in watts, that is, the lumens given per watt.

\[ \eta = \frac{860\ \mathrm{lumen}}{60\ \mathrm{W}} \]

\[ \eta = 14.3\ \mathrm{lumen/watt} \]

So the luminous efficiency is 14.3 lumen per watt, option (A). The options in watt per lumen give the inverse quantity, which is not the luminous efficiency, and 6.97 is not the ratio of 860 to 60. Higher luminous efficiency means more light for each watt, and a filament lamp of 14.3 lumen per watt is in the usual range for a 60 W bulb, far below that of a fluorescent lamp.

Your Answer : (Not Answered)

Correct Answer : D

A carpenter's hammer, such as the claw hammer, is specified by the weight of its head and the shape of the pein (the peen), which is the end of the head opposite the face, for instance the ball pein or cross pein. It is not specified by the length and width of the hammer, by the shape of the eye hole, which is only the hole in the head for the handle, or by the cross section of the cheek. The answer is weight and shape of the pein, option (D).

Your Answer : (Not Answered)

Correct Answer : B

Each cell is 1.5 V and 2 AH. To get 6 V the cells must be in series, and 6 / 1.5 = 4 cells per row. To get 4 AH the rows must be in parallel, since the capacity adds, and 4 / 2 = 2 rows. So 4 series cells and 2 rows are needed, which is 8 cells in all, option (B). The other options give the wrong voltage or capacity: 2 series cells would give only 3 V, 8 series cells would give 12 V, and 8 rows would give 16 AH.

Your Answer : (Not Answered)

Correct Answer : C

The power consumed by a resistive load such as an electric iron is the product of the voltage and the current, P = V x I.

\[ P = 240 \times 3 = 720\ \mathrm{W} \]

So the iron consumes 720 W, option (C), which is a reasonable rating for a small iron. The value 80 W is the voltage divided by the current, 240 W is the voltage alone, and 1120 W does not follow from the data given. A resistive appliance such as an iron takes the same power on AC as on DC at the same rms voltage, so the power factor is one and the simple product of volts and amperes can be used.

Your Answer : (Not Answered)

Correct Answer : D

By Kirchhoff's current law, the currents entering a node equal the currents leaving it. At the left node i1, i2 and i3, each 1 A, enter and i5 leaves, so i5 = 3 A. At the right node i5 and i6 enter, with i6 = 3 A, and i7 leaves, so

\[ i_{7} = i_{5} + i_{6} = 3 + 3 = 6\ \mathrm{A} \]

So i7 is 6 A, option (D). The values 0 A, 3 A and 4 A come from ignoring one of the currents or giving i6 the wrong direction. The same rule gives a quick check on the figure: the three incoming currents of 1 A each make 3 A in the middle, and then the 3 A from i6 adds to it.

Your Answer : (Not Answered)

Correct Answer : C

In the figure two 10 ohm resistors form a parallel pair at the top, so they give 5 ohms, and two 10 ohm resistors form a parallel pair at the right, which again gives 5 ohms. The two pairs are in series between the terminals a and b.

\[ R_{ab} = 5 + 5 = 10\ \Omega \]

So the equivalent resistance is 10 ohms, option (C). The value 5 ohms is the resistance of one pair only, and 15 and 20 ohms would need three or four resistors in series.

Your Answer : (Not Answered)

Correct Answer : B

Capacitors in series behave like resistors connected in parallel. For capacitors in series the reciprocal of the equivalent capacitance is the sum of the reciprocals, \(1/C_{eq} = 1/C_1 + 1/C_2 + \dots\), which is exactly the rule that resistors in parallel obey for their conductances. Resistors in series add directly (\(R_{eq} = R_1 + R_2 + \dots\)), so the first and third options describe the opposite behaviour: it is capacitors in parallel that add directly, like resistors in series. A galvanometer is a current-detecting instrument and has no connection with how capacitances combine.