- A force is said to be doing work on a system if it displaces the system from its initial position on which it acts.
- Work is not defined at a position or at an instant. It is defined for some displacement only.
- Work can be +ve, – ve or zero.
Suppose a block of mass ‘m’ placed on a rough horizontal plane is pulled by a constant force F acting at an angle θ to horizontal,
let Fsinθ < mg, then, N = mg – Fsinθ
Force needed to start the block moving is,
Fcosθ = fL
Using law of friction the limiting friction is,
fL = μS N
Combining above equations, we get,
Using tanα = μS, we get,
At θ = α, the force required to pull becomes minimum & given by
^Motion of a body on a fixed rough horizontal surface
Suppose a block of mass ‘m’ placed on a rough horizontal plane is pulled by a horizontal force F.
Following are the various possibilities:
Basic building blocks of digital electronics made of semiconducting material & used to control the flow of information from input to output in a logical manner & are used in calculators, digital watches, computers, robots, industrial control systems, and in telecommunications.
Semiconducting devices are the basic building blocks of all the modern electronic circuits & have following advantages over conventional vacuum tubes:
An oscillator is self sustained transistor amplifier with a positive feedback which produce electric oscillation of constant frequency
& amplitude without requiring any external input signal. It converts dc energy obtained from a battery into ac energy in same oscillatory circuit.
Transconductance is also called mutual conductance.
As β > > α, thus the ac power gain of a CEA is much larger than that of a CBA. Remember the transistor is not generating any power. The energy for the higher ac power at the output is supplied by the battery.
Both the junction are forward biased & here IC is maximum & does not depend on the input current IB.
Cut off state: Both the junctions are reverse biased as a result IC = 0. Between cut off & saturation state a transistor works as switch as here it turns over rapidly from OFF state (i.e. IC = 0 or cut off) to the ON state (i.e. IC is maximum or saturation state).
Active state: Emitter base junction is forward biased and the collector base junction is reverse biased. A transistor works as an audio amplifier in this regions.
Relation between α and β:
As the value of IB is about 1 – 5 % of IE or IC is 95 – 99 % of IE, α is about 0.95 and 0.99 and β is about 20 to 100. It is found that α and β are independent of current if the emitter base junction is forward biased and the collector base junction is reverse biased. Also the above definitions of α and β do not hold when both the junctions of a transistor are forward biased or reverse biased.
The CE configuration is frequently used as it gives high current gain as well as voltage gain.
It is a specially designed junction diode, which can operate in the reverse breakdown voltage region continuously without being damaged. In forward bias behaves like ordinary diode. Zener diode does not gets damaged at breakdown voltage, but it does so at some higher reverse voltage, known as its ‘burn out value’. The magnitude of zener voltage VZ can be decreased by increasing doping level in p and n type materials of zener diode.
I – V characteristics of a Zener diode are as shown. For a voltage more than zener breakdown voltage current through diode increases without increase in voltage across it. This feature is exploited to provide voltage stabilization across a circuit.
Suppose a load RL connected between a & b is connected to a fluctuating dc voltage supply Vs between c & d. Let the load can’t tolerate a voltage VL but the supply Vs can be more than VL. To protect the load from any increase voltage a zener diode of breaking voltage VZ = VL is connected to the input supply with a safety resistor RS in the input loop.
If at any time VZ increases than VL the zener diode works in the breakdown region increasing the current through it without increasing the voltage across it & thus the load always remains protected.