Electrical Work,Power and Energy Question & Answer 2024-Electronicsinfos

Electrical Work, Power and Energy Question & Answer 2024

What is a Mass?

It is the quantity of Matter possessed by a Body. The SI unit of Mass is Kg. The Mass of the body is a constant quantity and independent of the place and position of the body. Thus the body's mass is the same whether it is on the earth's surface, the Moon's Surface, On the top of a Mountain or down a deep well.

What is a Force?

Force is defined as the product of Mass and Acceleration. The Unit of Force is Newton.

 F = m＊a Newtons

m= mass of the body in kg

a= Accelerations in m/s²

What is a Waight?

The Force with which a body is attracted towards the centre of the earth is called the weight of the body.
Waight = m＊g newtons

Unit of Work Or Energy

Work is Said to be done on the body when a force acts on it and the body moves through some distance. The work done is stored in the body in the form of energy. Therefore work and power are measured in the same unit. The S.I. unit of work or energy is joule or newton-metre.

Cases of Mechanical Work or Energy 

It may be helpful to give an important case of work done or energy possessed in a mechanical system 

1.)  When a Force of F newtons is exerted on a body and the body moves through a distance 'd' metres in the direction of force, then 

Work done = F ＊d  joules or Nm

2.)  Suppose a force of F newtons is maintained tangentially at a radius of r metres from Origin. In one revolution the point of application of force travels through a distance of 2ℼr metres. 
Force ＊Distance moved in 1 revolution
F＊2ℼr
2ℼ ＊T Joules or Nm
Where T= F＊r is the torque.The S.I Unit of torque will be joules or Nm.

3.) If a Body of mass m kg is moving with a speed of v m/s, then kinetic energy possessed by the body is given by
K.E of the body = 0.5＊mv² joules

4.) If the body having a mass of m kg is lifted vertically through a height of h metres and g is the acceleration due to gravity in m/s², then
the potential energy of the body=work done in lifting the body=force required *height
Wight of the body height

mg*h=mgh

What is an Electrical Energy?

Electrical Energy is defined as when one coulomb is moved through a p.d of 1 volt. The S.I Unit of Electrical Work done or Electrical energy in joules.

1. Electrical Energy Expended= V*Q joules
2. Electrical Energy Expended=V*i*t Joules
   
3. Electrical Energy Expended=I²R*t Joules
   

Joules is also known as watt/sec
1 Kwh=1000 watt-hours=1000*3600 watt-sec
1 Kwh=36*10⁵ 

What is a Thermal Energy?

Thermal Energy was originally assigned the unit 'calorie'.One Calorie is defined as the amount of heat required to raise the temperature of 1 gm of water through 1℃. If S is the Specific heat of a body, then the amount of heat required to raise the 

temperature of m gm of the body 0℃ is given by

Heat gained =m*s*Ө Calories

It has been found experimentally that 1 calorie = 4.186 joules so heat energy in 

calories can be expressed in joules as under 

Heat gained =(msӨ)*4.186 joules

What are units of power?

The Rate of doing work is called power. In other words, power is the work done per unit of time Since work is measured in joules and the time in seconds, the unit of power will be watts or joules/sec.

1 Kw =1000 watts

for larger units we used 

1 Mw = 10⁶ watts

if a  body makes N r.p.m and the torque acting is T newton-metre, then 

Work done/sec = 2𝝿NT/60 j/s or watt

Heating Effect of Electrical Current 

When Electric current passes through a conductor, there is considerable 'friction' between the moving electrons and the molecules of the conductor. The Electrical Energy Supplied to the conductor to overcome this electrical friction is converted into heat.

This is known as the heating effect of electric current. For example, if I ampere is flowing through a conductor of a resistance R ohm For t Seconds, the Electrical energy supplied is I²Rt joules.

Heat Produced H =  I²Rt joules

Heat Produced H =  I²R/4.186 Calories

The heating effect of electric current is utilised in the manufacture of many heating appliances such as electric heaters, electric toasters, electric kettles, soldering irons etc. 

The Electrical energy in Kwh can be converted into joules by the following relation 

1 Kwh=36*10s⁵ joules 

A Heater coil is Cut into equal Parts and one of them is used in the heater. What is the ratio of heat produced by this half coil to that of the original coil?

For the Same p.d Heat produced per second, H=V²/R or H ∝ 1/R.

Let The Resistance of the original coil be R, Therefore resistance of the half coil is R/2

• For Half Coil,H₂∝ 1/(R/2)
• For Full coil, H₁∝1/R

H₂/H₁=R/R/2=2

The heat produced by the half coil will be doubled.

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