Dc means a direct current of any Dc circuit. Electricity may be defined as a form of energy. It involves making and using energy. It may also be defined as a way in which materials behave.
Similarly, the closed path followed by a direct current is called a d.c. circuit. A d.c. circuit essentially consists of a source of direct voltage (e.g. battery), the conductors used to carry current, and the load. a torch bulb (i.e. load) connected to a battery through conducting wires. The direct current starts from the positive terminal of the battery and comes back to the starting point via the load. The direct current follows the closed path ABCDA and hence ABCDA is a d.c. circuit. The load for a d.c. the circuit is usually resistant. In a d.c. circuit loads (i.e. resistances) may be connected in series or series-parallel.
The current that always flows in one direction is called direct current (d.c.). The current is supplied by a cell battery or d.c. the generator is direct current. (Fig.1.1 DC circuit), the battery supplies direct current to the bulb. The direction of the current is along ABCDA and it always flows in this direction. Note that direct current means steady direct current (i.e. one of constant magnitude) unless stated otherwise.
Some materials have an abundance of free electrons, which requires a low pressure to move them from atom to atom and establish a high current, such materials are known as good conductors. Other materials have few free electrons. In these the same electric pressure can move only a few electrons from atom to atom, establishing a low current. These are considered poor conductors.
The progressive motion of free electrons is hindered in all materials because they collide with atoms of the substance used. the opposition to the flow of electrons due to bonds between protons and electrons, as well as to collisions is called electrical resistance.
Resistance is analogous in most of its aspects to friction in mechanics or hydraulics and, like friction, results in heat generation. The heating of an electric iron or stove is due to the resistance of the heat-unit conductor materials. for safety the materials and cross-section of the conductors must be such that the temperature is kept well
Resistors in Series
A number of resistors are said to be connected in series if the same current flows through each resistor and there is only one path for the current to flow throughout. Consider three resistors of resistances R1, R2, and R3 connected in series across a battery of E volts as shown in fig. The total resistance Rt is given by ;
RT = R1+ R2 + R3,
Hence, when a number of resistances are connected in series, the total or equivalent resistance is equal to the sum of the individual resistances. Thus we can replace the series-connected resistor
shown in Fig. 2. with a single resistor, RT = ( R1 + R2 + R3). This will enable us to calculate the circuit current easily (I = E/RT).
(1) RT = R1+ R2 + R3
RT/V2 = R1/V2+ R2/V2 + R3/V2
or 1/PT = 1/P1+ 1/P2+ 1/P3
where PT is the total power dissipated by the series circuit and P1, P2 and P3 are the powers dissipated by individual resistors.
(2) The total conductance GT of the circuit is
GT = 1/RT = 1/R1 + R2 + R3
Also, 1/GT = 1/G1 + 1/G2 + 1 /G3
Here, G1 = 1/R1 ; G2 = 1/R2 ; G3 = 1/R3
The total power dissipated = I2 RT = I2/GT = E2GT
Resistors in Parallel
A number of resistors are said to be connected in parallel if the voltage across each resistor is the same and there are as many paths for current as the number of resistors. Consider three resistors of resistances R1, R2 and R3 connected in parallel across a battery of E volts as shown in Fig. 1.3. Then total resistance RT is given by ;
1/RT=1/R1+ 1/R2 + 1/R3
Hence, when a number of resistances are connected in parallel, the reciprocal of the total resistance is equal to the sum of reciprocals of individual resistances. Again, we can replace the parallel connected resistors shown in Fig. 1.3 with a single resistor RT.
(1) 1/RT= 1/R1 + 1/R2 + 1/R3
or V2/RT= V2/R1 +V2/R2+ V2/R3
or PT = P1+ P2+ P3
where is the total power dissipated by the parallel circuit and P1, P2 and P3 are the powers dissipated by individual resistors.
(2) The total conductance GT of the circuit is
GT = G1+ G2+ G3
Here, G1 = 1/R1 ; G2, = 1/R2 ; G3 = 1 /R3
We can also express currents I1, I2, and I3 in terms of conductances.
I1 = E/R1
I * G1/ G1 + G2 + G3
I2 =I * G2/G1 + G2 + G3 ; I3= I * G3/G1 + G2 + G3
The total power dissipated,
P = E2/RT = E2GT
Path of electrons in order to have electric current, electrons must move from atom to atom in which it is relatively easy for an electron to jump out of its orbit and begin to orbit in an adjoining or nearby atom. Substances that permit this movement of electrons are called conductors of electricity example, copper, aluminum, silver, etc.
The controlled movement of electrons, through a substance, is called current. Current occurs only when a difference of potential e.m.f or voltage is present. For example, we can get a difference in potential by connecting a battery to the ends of a length of copper wire. The pressure from the battery will then move the electrons.
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