Sonalika Pre-training Assessment Test

The controller creates three pseudo-sine waves. It does this by taking the DC voltage from the batteries and pulsing it on and off. In an AC controller, there is the additional need to reverse the polarity of the voltage 60 times a second. Therefore, you actually need six sets of transistors in an AC controller, while you need only one set in a DC controller. In the AC controller, for each phase you need one set of transistors to pulse the voltage and another set to reverse the polarity. You replicate that three times for the three phases — six total sets of transistors.

Opposite forces – Helicopters creates lift by pushing air down, thereby experiencing an upward reaction force. Birds and airplanes also fly by exerting force on air in a direction opposite to that of whatever force they need. The wings of a bird force air downward and backward in order to get lift and forward motion.

The law of conservation of energy, first formulated in the nineteenth century, is a law of physics. It states that the total amount of energy in an isolated system remains constant over time. The total energy is said to be conserved over time. For an isolated system, this law means that energy can change its location within the system, and that it can change form within the system, for instance chemical energy can become kinetic energy, but that energy can be neither created nor destroyed.

From: http://en.wikipedia.org/wiki/Conservation_of_energy

Inertia of motion – This is due to the inertia of the bodies to remain in the straight line. Due to this, the centrifugal force acts which pushes the passengers outwards

 In case of parallel field connection, it won’t rotate at all and will start humming and will create vibrations, as a torque produced by positive and negative cycle will cancel out each other. DC motor will be heated up and it may burn.

 If back emf vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. If supplying unit didn’t trip down by this time, excess current in armature may heat up the armature.

In case of DC motor, the speed is proportional to the back emf (Ea ∝ N). So, with the increase in speed, the back emf also increases. Therefore, armature current is also decreased, in case of series motor, armature current is equal to the line or load current.

All other parts except brushes and commutator are same in AC machine when outer looks are only taken in consideration. Commutator is used only in DC machine for providing mechanical rectification and not in AC machine.

Flemings laws can be summarized as whenever, a current carrying conductor comes under a magnetic field, there will be a force acting on the conductor and on the other hand, if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor.

In parallel combination, voltage remains same across two points.

 Charge

Electric current flows from a higher potential to lower potential.  When a circuit is connected using conductors, an electric field is established in the direction towards lower a potential point from a higher potential point. The electric field exerts an electric field on the electrons in the conductor in the opposite direction. So electrons drift in the opposite direction from – to + terminal.  We call direction of current to be opposite to the direction of motion of electrons.

An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field. Therefore, electrical resistance of insulators is infinitely high.

Power is the rate of flow of electrical energy through a conductor with potential diff n more energy is used for more resistance.

Commercial unit of electrical energy is defined as the energy consumed by any electronic appliance in an hour. The energy in watt-hour is the amplification of power in watts (unit) and time in hours.

Here, V = 220 V, I = 0.50 A
∴ Power (P) = VI = 220 x 0.50 = 110 W

Conductors are materials (mostly metals), which freely allow the passage of electrons through it. If electrons can flow freely through a material, it implies that even current can flow freely through that material since current is the rate of flow of electrons.

Potassium Hydroxide has very high ionic conductivity, due the high mobility of OH- anion in water solutions, itself due to its very low size. Besides, the concentration is increased for increasing the number of ions and therefore the ionic conductivity of the electrolyte.

Semi-conductors are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.

An ion is a charged atom or molecule. It is charged because the number of electrons do not equal the number of protons in the atom or molecule. An atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.

The accelerator pedal hooks to a pair of potentiometers (variable resistors), and these potentiometers provide the signal that tells the controller how much power it is supposed to deliver. The controller can deliver zero power (when the car is stopped), full power (when the driver floors the accelerator pedal), or any power level in between.

Running any electrical accessory reduces fuel economy, having the air conditioner on the maximum setting can cut efficiency 5 to 25 percent, according to the U.S. Department of Energy.