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An electromotive force is the potential differenceappearing across the terminals of a battery, generator, etc., when that device is not supplying any load. When the device is supplying a load current, the electromotive force is equal to the sum of the voltage drops around the complete circuit, including any internal voltage drop.
A potential difference (also known as a 'voltage'), as the name implies, is the difference in potential between two points.
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What is terminal PD?
A terminal potential difference is the potential difference appearing across the terminals of a voltage source, such as a battery or a generator, which varies according to the load supplied.When the battery or generator is off load (i.e. no load is connected to it), the terminal potential difference is equal to the electromotive force of that battery or generator.The terminal potential difference tends to decrease as the load current increases, due to a corresponding increase in the internal voltage drop of the battery or generator.
What metals are used in seebeck effect?
Bi, Ni, Pd, Pt,Cu, Mn, Hg, Pb, Sn, Au, Ag, Zn, Cd, Fe, Sb
What are the types of controllers?
P(Proportional )-controller I(Integral)-controller D(Derivative)-controller PI-controller PD-controller PID-controller Industrial controller ON-OFF controller
What is the Purpose of semiconductor compound in xlpe cables?
1) It is used for stress releaving at it will spead high voltage and not allowed to concentrate at or near to ground. 2) it is also helful in discharge as it work as a sensor in PD. Irfan Mulla Inspection Engineer, TUV-Nord (I) p Ltd. 09821236469
What is motoring mode of DC motor?
Read this Part I:DC Motor principles pg 1 Part I: Principles of DC Drive Control Learning Objectives: * to learn the basic characteristics of DC motors and their control parameters * to understand the various operating modes DCmotors and their representation: The basic principle of a DCmotor is the production of a torque as a result of the flux interaction between a "field" produced on the STATOR (either produced by a permanent magnet, or a field winding) and the current circulating in the "armature" windings on the ROTOR. In order to produce a torque of constant sign, the armature winding loops are connected to a set of "brushes" which commutate the current appropriately in each loop according to their geometric position. The commutator is a MECHANICAL RECTIFIER. Note that reversal of either the field current or the armature current results in a torque in the opposite direction. However, reversal of both fields does not change the torque direction, hence it can be used as a "universal motor" with DC or AC feed if both windings are in series. Basic Equations of a DC Machine: Steady state conditions (assume all time varying quantities have a constant average value) ( ) ( ) ( ) ( ) ( ) P T developed power T K I I A B T electrical torque V R I E R I K I armature voltage E K I Counter emf or Back EMF V R I fieldwinding d e e t f a load a a a a a v f v f f f f w w w w = = = + + = + = + = = (The back emf assumes that the magnetizing characteristic, E(If) is linear) Speed control: we can extract: v f a a a K I V - R I w = and one can control the speed with 1) Va "Voltage Control" 2) If "Field Control" 3) Ia (with If fixed) "Demand Torque" In practice, for speeds less than the base speed (rated), the armature current and field currents aremaintained at fixed values (hence constant torque operation), and the armature voltage controls the speed. For speeds higher than the base speed, the armature voltage is maintained at rated value, and the field current is varied to control the speed (note the hyperbolic characteristic). However, N +V (free wheeling diode) Armature Current (Rf, Lf) (La, Ra) Eo Rfc Field Control Resistor Fig 1: DC Motor Part I:DC Motor principles pg 2 this way the power developed Pd is maintained constant. This mode is referred to as "field weakening" operation. Case of Series Motor (or Universal Motor) In this case the field winding is series with the armature winding, hence If and Ia are equal. This leads to: v a a a f a K I V - (R + R )I w = One can either control the armature voltage (Voltage Control), or the armature current (Current Control) which is a measure of the torque control. Td , Pd Torque Power constant torque constant power speed Ia If Fig 2: Control Modes Torque Power constant torque constant power speed Td Ia Fig 3: DC Series Motor Control Part I:DC Motor principles pg 3 OperatingModes of DCMotors: Motoring: The back emf E < Va both Ia and If are positive. The motor develops a torque to meet the load torque. Dynamic Breaking: The voltage source is removed, and the armature is shorted. The kinetic energy stored in the rotor of the motor is dissipated in the armature resistance since the machine now works as a generator. Note here that theoretically, since the armature voltage is proportional to the speed, the motor would never stop... but in fact because there is also friction and viscous friction (windage), the motor will stop as soon as the speed is at a certain low value. Regenerative Breaking: The back emf E > Va , the machine acts as a generator, and the armature current flows towards the source, hence energy stored in the machine rotor is fed back to the source. Note however that this will cause the machine to slow down usually until E=Va and then revert to mode 1. Plugging: Plugging iswhen the field current is reversed, hence the back emf changes sign, and the equation of the machine becomes: a a a V = -E - R I hence a a a R I V E + = which means a very high torque generated in the opposite direction of rotation. Avery powerful breaking takes place. However it must be noted that the armature has to be opened as soon as the motor reaches zero speed, otherwise it will start rotating in the opposite direction. N +Va Rfc (La, Ra) E Ia (Rf, Lf) +Vf If Fig 4: Motoring Forward Tem w rated torque V1 V2 V3 V2 Tload FIG 5 torque speed V2 N +Va Rfc (La, Ra) E (Rf, Lf) +Vf Fig 6: Dynamic Breaking + Ia R V2 N +Va Rfc (La, Ra) E (Rf, Lf) +Vf Fig 7: Regenerative Breaking + Ia Part I:DC Motor principles pg 4 Two Transistor control of regenerative operation When the main switch opens, the armature current I(a1) has to be dissipated through the freewheeling diode. Then if one closes switch T1, the machine behaves as a generator with the energy stored in its inertia. Therefore the armature current I(a2)will start flowing and follws I(1). After a certain time one opens the switch T1, and the current I(a2) has to be redirected via diode D2 back to the source with I(2). This is because of the inductance of the machine acts as an emf restoring the flux stored in the magnetic field. Then one closes T1 again and so on. The chopping rate of switch T1 can be set in order to control the average current (Ia2), usually 1.5 times rated value. This is possible only if the speed is fast enough to provide terminal voltage. When the emf E reaches E=Ra.I(rated), the switch T1 remains closed for maximum breaking possible with the given emf. Four Quadrant Operation: Figure 8 summarizes the modes of operation in a four quadrant representation. Torque Speed Forward MOTORING Forward BREAKING Reverse BREAKING Reverse MOTORING Fig 8: 4 quadrant operation V2 N +Va (La, Ra) E Fig 7: Regenerative Control + T1 i2 i1 ia1 ia2 average Ia
Can terminal potential difference be greater than the emf supplied?
All cells have internal resistance. When connected to a load, the resulting load current results in an internal voltage drop across the internal resistance. This voltage drop acts in the opposite sense to the cell's e.m.f., thus causing its terminal voltage to fall below that of the e.m.f. The greater the load current, the greater the difference between the terminal voltage and the e.m.f.
Three similarities between pd and emf?
Both emf and pd have the same unit. namely volt Both have the same definition. It is the work performed in moving unit positive charge right from one point to the other against the electric field. Both are got by the product of current and resistance. But emf is the pd across of a cell or source when it is not in action. So emf is slightly greater than the pd in the circuit as there may be a little bit of internal resistance.
What is potensional difference PD EMF or voltage measured in?
They are each measured in volts (V).
What is the difference between emf pd?
The terminology E.M.F is the voltage output of a power source e.g a transformer bank, generator. As relates to potential difference it's a linear electrical field strenght between 2 points. E.g the charged plates of a capacitor.
Why a spark is produced in the switch of a fan when it is switched off?
when inductive load is switched off then current decreases as a result emf induced in the inductor or as whole of the circuit. There is air between switch and circuit wire. Emf tends to jump from higher pd to lower pd so air become ionised and spark is prouced
What does pd stand for in physics?
Pd in the periodic table stands for palladium.
What is terminal PD?
A terminal potential difference is the potential difference appearing across the terminals of a voltage source, such as a battery or a generator, which varies according to the load supplied.When the battery or generator is off load (i.e. no load is connected to it), the terminal potential difference is equal to the electromotive force of that battery or generator.The terminal potential difference tends to decrease as the load current increases, due to a corresponding increase in the internal voltage drop of the battery or generator.
What is the difference between a financial manager and a financial analyst?
Are there any difference between financial Management analyst and financial analyst? Series or job PD.
What is the difference between ra 6657 and pd 27?
putang ina mo gago ka
Why is there a difference in the number of alleles for hemophilia and redgreen colorblindness between males and females?
There is a difference in the number of alleles for hemophilia and red-green colorblindness, because when a carrier of protanomaly has a child with a deuteranomalic man. Denoting the normal vision alleles by P and D and the anomalous by p and d, the carrier is PD pD and the man is Pd. The daughter is either PD Pd or pD Pd. Suppose she is pD Pd. Thanks...
A battery of emf 2V is connected to an external resistance which is equal to its internal resistance and then find potential difference across the external resistance?
As the source impedance is equal to load impedance, it is assumed that both the resistances are in series. This distributes the whole voltage equally between both the impedance. Hence the PD across external resistance will be 1V.
What does water pd mean?
pressure difference
