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Basic Electrical Engineering Quiz | Cells and Batteries Quiz

April 16, 2019

Basic Electrical Engineering Quiz | Cells and Batteries Quiz


1. The chemical energy in a battery or cell
(a) is a form of kinetic energy.
(b) cannot be replenished once it is gone.
(c) changes to electrical energy when the cell is used.
(d) is caused by electric current.

 2. A cell that cannot be recharged is known as
(a) a dry cell.
(b) a wet cell.
(c) a primary cell.
(d) secondary cell.

 3. A Weston cell is generally used
(a) as a current reference source.
(b) as a voltage reference source.
(c) as a power reference source.
(d) as a fuel cell.

 4.The voltage produced by a battery of multiple cells connected in series is
(a) less than the voltage produced by a cell of the same composition.
(b) the same as the voltage produced by a cell of the same composition.
(c) more than the voltage produced by a cell of the same composition.
(d) always a whole-number multiple of 1.018 V.

 5. A direct short-circuit of a large battery can cause
(a) an increase in its voltage.
(b) no harm other than a rapid discharge of its energy.
(c) the current to drop to zero.
(d) a physical rupture or explosion.

 6. Suppose a cell of 1.5 V delivers 100 mA for 7 hours and 20 minutes, and then it is replaced
How much energy is supplied during this time?
(a) 0.49 Wh
(b) 1.1 Wh
(c) 7.33 Wh
(d) 733 mWh

 7. Suppose a 12-V automotive battery is rated at 36 Ah. If a 100-W, 12-V bulb is connected
across this battery, approximately how long will the bulb stay aglow, assuming the battery has been
fully charged?
(a) 4 hours and 20minutes
(b) 432 hours
(c) 3.6 hours
(d) 21.6 minutes

 8. Alkaline cells
(a) are cheaper than zinc-carbon cells.
(b) generally work better in radios than zinc-carbon cells.
(c) have higher voltages than zinc-carbon cells.
(d) have shorter shelf lives than zinc-carbon cells.

 9. The energy in a cell or battery depends mainly on
(a) its physical size.
(b) the current drawn from it.
(c) its voltage.
(d) all of the above.

 10. In which of the following devices would a lantern battery most likely be found?
(a) A heart pacemaker
(b) An electronic calculator
(c) An LCD wall clock
(d) A two-way portable radio

 11. In which of the following devices would a transistor battery be the best power choice?
(a) A heart pacemaker
(b) An electronic calculator
(c) An LCD wall clock
(d) A two-way portable radio

 12. For which of the following applications would you choose a lithium battery?
(a) A microcomputer memory backup
(b) A two-way portable radio
(c)A stand-alone solar-electric system
(d) A rechargeable lantern

 13. Where would you most likely find a lead-acid battery?
(a) In a portable audio CD player
(b) In an uninterruptible power supply
(c) In an LCD wall clock
(d) In a flashlight

 14. A cell or battery that maintains a constant current-delivering capability almost until it dies is
said to have
(a) a large ampere-hour rating.
(b) excellent energy capacity.
(c) a flat discharge curve.
(d) good energy storage capacity per unit volume.

 15. Where might you find a nickel-based battery?
(a) In a satellite
(b) In a portable cassette player
(c) In a handheld radio transceiver
(d) More than one of the above

 16. A disadvantage of mercury cells and batteries is the fact that
(a) they don’t last as long as other types.
(b) they have a flat discharge curve.
(c) mercury is destructive to the environment.
(d) they need to be recharged often.

 17. Which kind of battery should never be used until it dies?
(a) Silver-oxide
(b) Lead-acid
(c) Nickel-based
(d) Mercury

 18. The useful current that is delivered by a solar panel can be increased by
(a) connecting capacitors in parallel with the solar cells.
(b) connecting resistors in series with the solar cells.
(c) connecting two or more groups of solar cells in parallel.
(d) connecting resistors in parallel with the solar cells.

 19. An interactive solar power system
(a) allows a homeowner to sell power to the electric company.
(b) lets the batteries recharge at night.
(c) powers lights, but not electronic devices.
(d) is totally independent from the electric company

 20. An advantage of methanol over hydrogen for use in fuel cells is the fact that
(a) methanol is the most abundant element in the universe.
(b) methanol is not flammable.
(c) methanol is a solid at room temperature.
(d) methanol is easier to transport and store.

Answers


 1. c 2. c 3. b 4. c 5. d 6. b 7. a 8. b 9. a 10. d 11. b 12. a 13. b 14. c 15. d 16. c 17. c 18. c 19. a 20. d

Basic Electrical Engineering Quiz | Cells and Batteries Quiz Basic Electrical Engineering Quiz | Cells and Batteries Quiz Reviewed by Sikha on April 16, 2019 Rating: 5

Current Electricity objective questions in Electrical Engineering

October 27, 2018

Current Electricity objective questions in Electrical Engineering



The substances which have a large number of free
electrons and offer a low resistance are called
(a) insulators
(b) inductors
(c) semi-conductors
(d) conductors
Ans: d

Out of the following which is not a poor conductor ?
(a) Cast iron
(b) Copper
(c) Carbon
(d) Tungsten
Ans: b

Out of the following which is an insulating material ?
(a) Copper
(b) Gold
(c) Silver
(d) Paper
Ans: d

Conductance is reciprocal of
(a) resistance
(b) inductance
(c) reluctance
(d) capacitance
Ans: a

With rise in temperature the resistance of pure metals
(a) increases
(b) decreases
(c) first increases and then decreases
(d) remains constant
Ans: a

With rise in temperature the resistance of semiconductors
(a) decreases
(b) increases
(c) first increases and then decreases
(d) remains constant
Ans: a

The resistance of a copper wire 200 m long is 21 Q. If its
thickness (diameter) is 0.44 mm, its specific resistance is
around
(a) 1.2 x 10~8 Q-m
(b) 1.4 x 10~8 Q-m
(c) 1.6 x 10″”8 Q-m
(d) 1.8 x 10″8 Q-m
Ans: c

An instrument which detects electric current is known
as
(a) voltmeter
(b) rheostat
(c) wattmeter
(d) galvanometer
Ans: d

A light bulb draws 300 mA when the voltage across it is
240 V. The resistance of the light bulb is
(a) 400 Q
(b) 600 Q
(c) 800 Q
(d) 1000 Q
Ans: c

In a circuit a 33 Q resistor carries a current of 2 A. The
voltage across the resistor is
(a) 33 V
(b) 66 v
(c) 80 V
(d) 132 V
Ans: b

Four wires of same material, the same cross-sectional
area and the same length when connected in parallel give a
resistance of 0.25 Q. If the same four wires are connected is
series the effective resistance will be
(a) 1 Q
(b) 2 Q
(c) 3 Q
(d) 4 Q
Ans: d

Which of the following material has nearly zero
temperature co-efficient of resistance?
(a) Manganin
(b) Porcelain
(c) Carbon
(d) Copper
Ans: a


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Current Electricity objective questions in Electrical Engineering Current Electricity objective questions in Electrical Engineering Reviewed by Sikha on October 27, 2018 Rating: 5

Cyclotron

August 13, 2017
Cyclotron




Cyclotron is a machine to accelerate charged particles or ions to high energies. It was invented by E.O Lawrence and M.S Livingston.
  • Cyclotron uses both electric and magnetic fields in combination to increase the energy of charged particles.
  • The electric and magnetic fields are perpendicular to each other ( and called as crossed fields)
  • Principle:- the frequency of revolution of the charged particle in a magnetic field is independent of its energy.

Working:
o   The particles move most of the time inside two semi circular disc –like metal containers, D1   and D2 , which are called ‘dees’  ( as they look like the letter ‘D’)
o   Inside the metal boxes, the particle is shielded and is not acted on by the electric field.
o   The magnetic field acts on the particle and makes it go round in a circular path inside the dee.
o   Every time the particle moves from one dee to another, it is acted upon by the electric field.
o   The sign of the electric field is changed alternately in tune with the circular motion of the particle.
o   Thus, the particle is always accelerated by the electric field
o   Each time, the acceleration increases the energy of the particle.
o   As energy increases, the radius of the circular path also increases. So, the path is a spiral one.
o   The whole assembly is evacuated to minimize collisions between the ions and the air molecules.
o   A high frequency a.c voltage is applied to the dees.


In the fig, positive ions or positively charged particles (protons) are released at the centre P. They move in a semi-circular path in one of the dees and arrive in the gap between the dees in a time interval T/2.
T- period of revolution.
T=1/fC = 2Ï€m/qB
Or , fC = qB/2 πm
fC – Cyclotron frequency
fa – frequency of applied voltage
At resonance, fC = fa
  • The phase of the supply is adjusted so that when the positive ions arrive at the edge of D1,   the dee D2 is at a lower potential and the ions are accelerated across the gap.
  • Inside the dees, the particles travel in a region free of the electric field.
  • The increase in their K.E = qV each time they cross from one dee to another.
  • (V= the voltage across the dees at that time)
  • Thus, radius of the path increases each time they cross the dees.
  • The ions are repeatedly accelerated across the dees until they have the required energy to have a radius approximately equal to that of the dees.
  • They are then deflected by a magnetic field and leave the system via an exit slip.
From  





Applications
  1. Used to bombard nuclei with energetic particles to accelerate nuclei and study the resulting nuclear reactions
  2. Used to implant ions in to solids and modify their properties. Or to synthesize new materials.
  3. Used in hospitals to produce radio active substances that can be used in diagnosis and treatment.




Cyclotron Cyclotron Reviewed by Sikha on August 13, 2017 Rating: 5

Synchronous Motor- Advantages, disadvantages and applications

August 13, 2017
Synchronous Motor- Advantages, disadvantages and applications

Advantages:
1.     Its power factor can be controlled by the control of field current.
2.     In certain applications, the fact that its speed is independent of load and applied voltage, may be important.
3.     It’s efficiency is slightly higher than that of induction motor.
4.     For low speeds and high rating, ( above 500 kW) a synchronous motor is cheaper than induction motor

Disadvantages:
1.     The need of dc source for excitation (usually a an exciter is mounted on the shaft to provide the excitation)
2.     Need of starting and synchronizing
3.     Instability
4.     Hunting
5.     Need of expensive control devices


In view of the above advantages, and  disadvantages, the synchronous motors are used only for low speed, high up speed, high hp requirements.

Applications:

1.     Large low head pumps
2.     Rubber mills and mixers
3.     Crushers
4.     Paper mill drives
5.     Compressors
6.     Rolling mills
7.     Ball mills etc
8.     Synchronous motor can also be used as a phase modifier for voltage regulation of transmission lines.


Synchronous Motor- Advantages, disadvantages and applications Synchronous Motor- Advantages, disadvantages and applications Reviewed by Sikha on August 13, 2017 Rating: 5
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