what is the resistance of earth(good ground)?

Earth is  a good  conductor, it has less than 5 ohms of resistance.

T Flip Flop used as frequency divider

Similarly To D FF,T FF also used as frequency divider.

D Flip Flop as a Frequency divider how?

D FF called as binary divider or frequency divider by small changes in circuit.
By connecting complement output Q(not Q) to input D,then its output is divided the input with a factor of 2.so it is called as frequency divider.

Inductor blocks AC why?

In regulator circuits, inductor is connected in series with rectifier circuits for blocking AC.
Inductor is allows Direct current(low frequency) and blocks alternating current(AC) this is because of inductive reactance.

Inductive reactance is XL=2pif.

If frequency f is high,inductive reactance also high so it blocks high frequency signal.it means high frequency alternating current(AC) is blocked by inductor.

similarly,if frequency f is low,inductive reactance is low so it allows low frequency signal.it means low frequency direct current(DC) is allowed by inductor.

capacitor blocks dc why?

capacitors are connected in series in amplifier circuits for blocking dc from input.this means capacitor blocks direct current(low frequency) and allows alternating current(high frequency).
this is because of capacitive reactance Xc=1/2pif

 if input frequency f is high,the reactance of a capacitor becomes low so it allows a signal passing through it.it means high frequency alternating current(AC) is allowed by a capacitor.

similarly,if input frequency f is low,the reactance of a capacitor becomes high so it not allows low signal passing through it.it means low frequency direct current(DC) is not allowed by a capacitor.

negative resistance property

In resistor,when input applied voltage increases it causes electric current also increases through in it because of ohms law,this property is called positive resistance of element or circuit.but here is negative resistance property,if applied voltage increases it causes decreases electric current through in it,it is called negative resistance of a element or circuit.

EX: uni junction transistor(UJT),tunnel diode,gunn diode, thyristors, IMPATT, magnetrons etc.

*Advantages of negative resistance:
 
1.used in oscillators. UJT oscillator,gunn diode oscillator.
2.mainly used in high frequency oscillators in microwave applications.

linear and non linear circuits

LINEAR ELEMENT AND LINEAR CIRCUIT:

If the input signal is passed through the linear elements in the circuit,the circuit in which the circuit parameters(resistance,inductance,capacitance,waveform,frequency etc) are constant, that is the output is following input signal, that circuit is called linear circuit and that device called linear device.
simply circuit parameters are not changed by applied input signal is called linear circuit.
the output response of circuit is directly proportional to input signal.

Ex: resistors and resistive circuits.
 inductors and inductive circuits.
 capacitor and capacitive circuits.

NON LINEAR ELEMENT AND NON LINEAR CIRCUITS:

If the input signal is passed through the non linear elements in the circuit,the circuit in which the circuit parameters (resistance,capacitance,inductance,waveform,frequency etc) are not constant, that is the output is not following the input,that circuit is called non linear circuit and that device is called non linear device.
circuit parameters are changed by applied input signal is called non linear circuit.
the output response of circuit is not directly proportion to input signal.

Ex:diodes,transistors,transformers etc.

FET is voltage controlled device why?

Field effect Transistor output characteristics are depends on input voltage applied at gate source terminal that's why it is called as voltage controlled device. 

BJT is current control device why?

The output characteristics of BJT is depends on input current that's why BJT is called current controlled device.

voltmeter connected in parallel in circuit why?

voltmeter is connected in parallel in the circuit because of  voltmeter have very high resistance and if it is connected in series in the circuit all voltage drops at voltmeter it self and no voltage at load or output.hence voltmeter connected in parallel in the circuit only.

Ammeter connected in series in circuit why?

Ammeter always connected in series in the circuit because of ammeter have very low resistance, and if it is connected in parallel,it would be short circuit so no current at output, hence ammeter always connected in series in circuit.

Rectifiers

Q: what is rectifier?why we using or importance?

A: Rectifier is an electronic circuit which converts Alternating current into Direct Current.
  In order to work electronics devices requires dc supply but we have Ac supply every where,so we need first convert AC into DC for this we use rectifiers.
 Rectifiers are half wave and full wave.

Resistors

The property of a conductor which opposes the flow of current is Resistor.It control the amount of current the runs through them.on resistor body 5 band of colours are printed. units are ohms.

The circuit symbol is-

*Features of resistors:

1.These are two terminal,passive bilateral elements.
2.The effect of resistance is same for both AC and DC.

* Common uses of Resistors:

1.to limit the current.
2.to establish proper values of circuit voltages due to IR drops.
3.to provide load. etc

*Types of resistors

                                                                 resistors                                                                                                    
                         1.fixed                                                                   2.variable

      a.carbon   i.carbon composition(solid type)             a,general purpose        i. Potentiometers (Pots)
                      ii.carbon film(film type)                                                              ii.rheostats
      b.precision                                                                b.precision type           i.LDRs
                      i.wire wound                                                                                ii.Thermistors
                     ii.metal film                                                                                  iii.Varistors
      c.wire wound(power type)                                                                           iv.Trimmers

*specifications of resistors:

1.resistance value
2.tolerance
3.power rating
4.temperature coefficient of resistance
5.voltage coefficient
6.high frequency performance
7.noise figure
8.stability
9.size,shape and leads.

*resistor colour coding:

Ex: brown ,black ,red, gold
         1            0   100   5%
       
            10*100=1k

                 
 

 Electronics is branch of science which deals with flow of current. electronics deals with electrical circuits that involve active components such as vacuum tubes, transistors, diodes, integrated circuits and passive components such as resistors, inductors and capacitors.
          Communication is transferring information from one place to another.
For proper communication using antennas for wireless communication and cables, fibers etc for wire communication.

about electronics

Electronics is branch of science which deals with flow of current. electronics deals with electrical circuits that involve active components such as vacuum tubes, transistors, diodes, integrated circuits and passive components such as resistor, inductor and capacitor.