February 2018

Archive for February 2018

When an electric current passes through a metallic conductor, its temperature rises. This is due to

A. collisions between conduction electrons and atoms
B. the release of conduction electrons from parent atoms
C. mutual collisions between metal atoms
D. mutual collisions between conducting electrons

Answer: A

If the efficiency of a machine is to be high, what should be low?

A. Input power
B. Losses
C. True component of power
D. kWh consumed
E. Ratio of output to input

Answer: B

Resistance of a material always decreases if

A. temperature of material is decreased
B. temperature of material is increased
C. number of free electrons available become more
D. none of the above is correct

Answer: C

Electric current passing through the circuit produces

A. magnetic effect
B. luminous effect
C. thermal effect
D. chemical effect
E. all above effects

Answer: C

Resistance of a tungsten lamp as applied voltage increases

A. decreases
B. increases
C. remains same
D. none of the above

Answer: B

An electric filament bulb can be worked from

A. D.C. supply only
B. A.C. supply only
C. Battery supply only
D. All above

Answer: D

In an electric kettle, water boils in 10 m minutes. It is required to boil the boiler in 15 minutes, using same supply mains

A. length of heating element should be decreased
B. length of heating element should be increased
C. length of heating element has no effect on heating if water
D. none of the above

Answer: A

A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the heater output will

A. decrease
B. increase
C. remain same
D. heater will burn out

Answer: B

Which of the following quantities remain the same in all parts of a series circuit?

A. Voltage
B. Current
C. Power
D. Resistance

Answer: B

The thickness of insulation provided on the conductor depends on

A. the magnitude of voltage on the conductor
B. the magnitude of current flowing through it
C. both A. and (b)
D. none of the above

Answer: A

The insulation on a current carrying conductor is provided

A. to prevent leakage of current
B. to prevent shock
C. both of above factors
D. none of above factors

Answer: C

Heat in a conductor is produced on the passage of electric current due to

A. reactance
B. capacitance
C. impedance
D. resistance

Answer: D

The hot resistance of the bulb's filament is higher than its cold resistance because the temperature co-efficient of the filament is

A. zero
B. negative
C. positive
D. about 2 ohms per degree

Answer: C

A closed switch has a resistance of

A. zero
B. about 50 ohms
C. about 500 ohms
D. infinity

Answer: A

What will be energy used by the battery if the battery has to drive 6.28 x 1018 electrons with a potential difference of 20 V across the terminal?

A. 5 joules
B. 10 joules
C. 15 joules
D. 20 joules

Answer: D

Two resistances Rl and Ri are connected in series across the voltage source where Rl>Ri. The largest drop will be across

A. Rl
B. Ri
C. either Rl or Ri
D. none of them

Answer: A

The four bulbs of 40 W each are connected in series swift a battery across them, which of the following statement is true?

A. The current through each bulb in same
B. The voltage across each bulb is not same
C. The power dissipation in each bulb is not same
D. None of the above

Answer: A

Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns open

A. there will be heavy current in the main line
B. rest of the two bulbs will not light
C. all three bulbs will light
D. the other two bulbs will light

Answer: D

If a wire conductor of 0.2 ohm resistance is doubled in length, its resistance becomes

A. 0.4 ohm
B. 0.6 ohm
C. 0.8 ohm
D. 1.0 ohm

Answer: A

If a parallel circuit is opened in the main line, the current

A. increases in the branch of the lowest resistance
B. increases in each branch
C. is zero in all branches
D. is zero in the highest resistive branch

Answer: C

The resistance of a few meters of wire conductor in closed electrical circuit is

A. practically zero
B. low
C. high
D. very high

Answer: A

Which of the following statement is true?

A. A galvanometer with low resistance in parallel is a voltmeter
B. A galvanometer with high resistance in parallel is a voltmeter
C. A galvanometer with low resistance in series is an ammeter
D. A galvanometer with high resistance in series is an ammeter

Answer: C

A 3 Q resistor having 2 A current will dissipate the power of

A. 2 watts
B. 4 watts
C. 6 watts
D. 8 watts

Answer: C

The filament of an electric bulb is made of

A. carbon
B. aluminium
C. tungsten
D. nickel

Answer: C

In a series circuit with unequal resistances

A. the highest resistance has the most of the current through it
B. the lowest resistance has the highest voltage drop
C. the lowest resistance has the highest current
D. the highest resistance has the highest voltage drop

Answer: D

The minimum charge on an ion is

A. equal to the atomic number of the atom
B. equal to the charge of an electron
C. equal to the charge of the number of electrons in an atom (#) zero

Answer: B

The rating of a fuse wire is always expressed in

A. ampere-hours
B. ampere-volts
C. kWh
D. amperes

Answer: D

Insulating materials have the function of

A. preventing a short circuit between conducting wires
B. preventing an open circuit between the voltage source and the load
C. conducting very large currents
D. storing very high currents

Answer: B

Varistors are

A. insulators
(6) non-linear resistors
C. carbon resistors
D. resistors with zero temperature coefficient

Answer: B

Which one of the following does not have negative temperature co-efficient?

A. Aluminium
B. Paper
C. Rubber
D. Mica

Answer: A

A resistance having rating 10 ohms, 10 W is likely to be a

A. metallic resistor
B. carbon resistor
C. wire wound resistor
D. variable resistor

Answer: C

All of the following are equivalent to watt except

A. (amperes) ohm
B. joules/sec.
C. amperes x volts
D. amperes/volt

Answer: D

For which of the following 'ampere second' could be the unit?

A. Reluctance
B. Charge
C. Power
D. Energy

Answer: B

Which is the best conductor of electricity?

A. Iron
B. Silver
C. Copper
D. Carbon

Answer: B

Ohm's law is not applicable to

A. vacuum tubes
B. carbon resistors
C. high voltage circuits
D. circuits with low current densities

Answer: A

Which of the following materials has a negative temperature co-efficient of resistance?

A. Copper
B. Aluminum
C. Carbon
D. Brass

Answer: C

Which of the following statement is true both for a series and a parallel D.C. circuit?

A. Elements have individual currents
B. Currents are additive
C. Voltages are additive
D. Power are additive

Answer: D

Two resistors are said to be connected in series when

A. same current passes in turn through both
B. both carry the same value of current
C. total current equals the sum of branch currents
D. sum of IR drops equals the applied e.m.f.

Answer: A

You have to replace 1500 Q resistor in radio. You have no 1500 Q resistor but have several 1000 Q ones which you would connect

A. two in parallel
B. two in parallel and one in series
C. three in parallel
D. three in series

Answer: B

Which of the following material has nearly zero temperature co-efficient of resistance?

A. Manganin
B. Porcelain
C. Carbon
D. Copper

Answer: A

Current velocity through a copper conductor is

A. the same as propagation velocity of electric energy
B. independent of current strength
C. of the order of a few ^.s/m
D. nearly 3 x 108 m/s

Answer: C