ANSWERS A YOUR KNOWLEDGE IN FUNDAMENTAL ELECTRONICS

Created it, 06/02/21

Last update it, 06/02/22

Return to the site            To contact the author

Answers 1 Answers 2 Answers 3 Answers 4 Answers 5 Answers 6 Answers 7 Answers 8 Answers 9 Answers 10

Answers to the test N° 1

1 - The fundamental law of electrostatics is stated in the following way: The loads of contrary signs attract each other while the of the same loads sign are pushed back.

2 - The molecule is the smallest quantity of a substance being able to exist without this substance not losing its particular characteristics.

3 - The loads had by the protons are positive “+”, and those had by the electrons are negative “-”.

4 - The law relating to the forces being exerted between two magnetic poles is stated in the following way : Two poles of comparable nature are pushed back while two poles of different nature attract each other.

5 - A magnetic field is part of the space in which appear magnetic actions.

6 - The materials whose atoms have a very incomplete external orbit are conductive.

7 - In a solid driver, the electrical current is consisted a displacement of electrons, whereas in a liquid, it is consisted a displacement of ions.

8 - The negative ions are called also anions because they move towards the anode and the positive ions are also called cations because they move towards cathode.

9 - The conventional direction of the electrical current is the reverse of the displacement of the electrons, it is directed “+” towards “-”.

10 - The intensity of the electrical current in a driver is given by the quantity of electricity which, to each second, passes through the section of this driver. Its unit is the amp and its symbol I.

Answers to the test N° 2

1 - The potential and the tension are measured in Volt.

2 - The four essential elements of a pile are: two electrodes made out of different materials, the electrolytic solution and depolarizing substance.

3 - The electric resistance of a driver is the obstacle offered by this driver to the passage of the electrical current.

4 - The resistance of a driver is calculated by multiplying the resistivity of material used, by the length of the driver and while dividing by its section. R = (p x L) / S.

5 - By electric conductance, one understands the aptitude of a driver to lead the electrical current more or less well.

6 - The measuring units of the resistivity and conductivity are respectively the ohmmeter and the mho/meter.

7 - The three forms of the law of Ohm are stated in the following way :

a) Resistance is obtained by dividing the tension by the current :  R = V / I

b) The tension is obtained by multiplying the current by resistance :  V = R x I

c) The current is obtained by dividing the tension by resistance :  I = V / R

8 - The connections in series show the specific characteristic to have all the elements traversed by the same current, while the connections in parallel, it there with the same terminal voltage of each element.

9 - The f.e.m. (electromotive force) of a pile is the tension present between its electrodes when the pile does not output any current.

10 - The association of piles in series makes it possible to obtain a f.e.m. equal to the sum f.e.m. of each pile.

11 - The electric output can be calculated in three ways :

a) By multiplying the tension by the current :  P = V x I

b) By multiplying resistance by the square of the current :  P = R x I²

c) By dividing the square of the tension by resistance :  P = V² / R

12 - The power consumption by an electrical appliance functioning during a given time is obtained by multiplying its power expressed in Watt per time in second. This energy is expressed in of joule.

13 - The calorie is the measuring unit of the quantity of heat and is defined as being the quantity of heat necessary to raise the temperature of one gram water of 1° C.

14 - The quantity of heat in calories is calculated while multiplying by 0,238 the power consumption in joule to produce it.

15 - In addition to the resistive value, an electric resistance is characterized by the maximum power which it is able to dissipate without being damaged

Answers to the test N° 3

1 - The electric capacity of a body indicates the quantity of electricity which it must have to reach the potential of 1 volt.

2 - The permittivity relating to the air or the vacuum indicates how much time the capacitance of a capacitor to air increases if one introduces between his reinforcements a dielectric other that the air. Its symbol is er, and it does not have a unit.

3 - The property first of a condenser is to store the electric power and, for this reason, it is called : preserving element.

4 - Only half of the energy which a pile provides to charge a condenser is stored by this one.

5 - The energy stored by a condenser is calculated by multiplying the capacity by the square of the tension present at its terminals and by dividing the result by 2:  Wc = (C x V²) / 2

6 - Half of the energy which is not stored by a condenser dissipates (transforming itself into heat) inside the pile, because of its internal resistance.

7 - It is said that there is electric field in a determined zone, when an electric charge placed in this zone is subjected to a force of electric nature.

8 - The intensity of the existing electric field in the dielectric one of a condenser is calculated by dividing the tension between the reinforcements by the distance which separates them.

9 - The tension of service of a condenser indicates the tension which one should not exceed during its operation in order not to cause the destruction by breakdown, of its dielectric.

10 - The equivalent capacity several condensers connected in parallel is obtained by adding the capacity with each condenser.

11 - The equivalent capacity several condensers connected in series is obtained by applying the formula :

12 - The formula of two condensers connected in series is :

Answers to the test N° 4

1 - The magnetic effect of the electrical current consists of the production of a magnetic field around any driver crossed by this electrical current.

2 - The magnetomotive force is the product of the number of whorls by the electrical current which crosses them : f.m.m. = N x I

3 - The flow of induction is consisted of the whole of the lines of induction.

4 - The inductance of a reel is obtained by dividing the flow embraced by its whorls, by the current which traverses them.

L = F / I

5 - The magnetic capacity of materials is determined by their absolute magnetic permeability µ.

6 - The inductance of a reel is related to four parameters :

• its number of whorls N

• its section S

• its length L

• the absolute magnetic permeability of its core µ

L = µ x (N² x S) / l

Answers to the test N° 5

1 - We edge induce has f.e.m. in A whorl while varying the flow off induction embraced by this whorl.

2 - The been worth off the induced f.e.m. depend, not only off the variation off embraced flow goal have time off have this variation lasts.

3 - The Lenz's law is stated in the following way : the current induces has direction such, which it is opposed to the causes which gave him birth.

4 - Mutual induction is distinct year electromagnetic phenomenon which appears between two circuits, while the self induction is year electromagnetic phenomenon of induction which appears in A individual circuit.

5 - In the box of has real, the law of NEUMANN is stated in the following way : The f.e.m. of self induction is obtained by multiplying inductance by the variation of the current and by dividing this product by time that this variation lasts :

E = (L x I)  / t

6 - Inductance equivalent to two or several reels connected in series is obtained by adding inductances with each reel.

7 - Equivalent inductance several reels connected in parallel is given by the formula :

8 - The electric power stored by a reel is calculated by multiplying the inductance of the reel by the square of the current and while dividing by 2 the product obtained.

WL = (L x I²) / 2

Answers to the test N° 6

1 - The difference between the AC current and the D.C. current is as follows : 

• While the D.C. current always circulates in the same direction, the AC current changes its direction of circulation periodically.

2 - A AC current produced by an inductive flow turning takes a sinusoidal form.

3 - The chart of a AC current is used at every moment to indicate the intensity taken by the current.

4 - The period of a AC current is the time put by this current to achieve a complete cycle.

5 - The frequency of a AC current indicates the number of complete cycles achieved by this current in one second. The unit of the frequency is the hertz.

6 - The period of a AC current is obtained by taking the reverse of the frequency.

T = 1 / F

7 - The effective value of a AC current is the intensity of a D.C. current which would produce in same resistance the same quantity of heat as this AC current.

The effective value of a AC current is related to its maximum value by the relation :

Answers to the test N° 7

1 - For the alternating voltage, one generally indicates the effective value.

2 - In a capacitive circuit, it cannot circulate of D.C. current.

3 - The AC current which circulates in a capacitive circuit is due to the loads and successive discharges of the condenser. (The AC current never crosses in a condenser because of the dielectric one and it blocks any passage of the D.C. current).

4 - In a capacitive circuit, the current has out of phase a lead of a quarter of period over the tension.

5 - By angle of dephasing, one understands the angle ranging between the two vectors which represent the tension and the current.

6 - The capacitive reactance (Xc) is resistance offered by a condenser to the current ; it is calculated by means of the formula:

7 - In an inductive circuit, the tension is out of phase advances some on the current.

8 - The pulsation (w) of an alternative size is the product of the constant 2 x p by the frequency F :  w = 2 x p x F    

9 - The inductive reactance (XL) is calculated by means of the formula:  XL = 2 x p x F x L = w x L

10 - The measuring unit of the capacitive and inductive reactance is the ohm (W)

Answers to the test N° 8

1 - The obstacle which is opposed in the passing of the current is the impedance.

2 - The value of impedance (Z) is given by the relation :  

3 - The impedance is measured in ohms.

4 - The shapes of closed cores usually used are those of the types “with column” and “battleship”.

5 - It is said that a ferromagnetic core is more permeable than the air with the lines of induction because they cross it more easily.

6 - The flow of dispersion represents the whole of the lines of induction which “escape” the ferromagnetic core and which are closed again through the air.

7 - A magnetic circuit is consisted a rolling up around a ferromagnetic core.

8 - The magnetic reluctance indicates the number of ampere turns necessary to obtain a flow of induction of Wb in the core : (Wb = Weber).

9 - It is calculated by dividing the length of the core by its section and the absolute permeability of ferromagnetic material.

10 - The core is saturated when the flow of induction does not increase any more, whereas the f.m.m. continues to grow.

Answers to the test N° 9

1 - Two rollings up of a transformer are called primary education and secondary.

2 - A transformer functions in neutral when its secondary is open.

3 - A transformer cannot function with the D.C. current, it functions only with the AC current.

4 - The report/ratio of transformation of a transformer is obtained by dividing the secondary tension by the primary tension.

5 - The report/ratio of transformation is equal to the number of secondary whorls, divided by the number of primary whorls.

6 - By universal primary education, one understands a primary education provided with catches adapted to all the possible values of the tension of the network.

7 - The charging current of a transformer is the current one provided to the load by the secondary.

8 - The core of the transformers is formed small sheets insulated between them, to reduce the losses of power due to the eddy currents.

9 - Induction is the flow which crosses each square centimetre of the section of a ferromagnetic core.

10 - The auto-transformer is especially more advantageous than the transformer when his report/ratio of transformation is close to 1.

Answers to the test N° 10

1 - The operation of a galvanometer is due to the magnetic effect.

2 - The gauge of a measuring apparatus is the maximum value which it can measure.

3 - The internal resistance of a galvanometer is the resistance presented by the driver constituting the mobile reel.

4 - To measure the current which circulates in a circuit, one connects the galvanometer in series with the circuit.

5 - To double the gauge of a galvanometer, for the measurement of the current, one must connect to him in parallel a shunt whose resistance is equal to the internal resistance of the galvanometer.

6 - To measure the tension at the ends of a resistance, one connects the voltmeter in parallel on this resistance.

7 - The value which one must give to the additional resistance of a voltmeter obtains by dividing the maximum tension that one wants to measure by the current of end of scale of the apparatus and by withdrawing result obtained his internal resistance.

Rad = (Vmax / I) - r

8 - The zero are at the right end of the dial of the ohmmeter.

Return to the site            To contact the author

Daniel