√√ Net Resistance in Series and Parallel Circuits | Electrical Energy in the Home | iitutor

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Net resistance in series and parallel ciruits

Factors that affect resistance

The cause of resistance

Why should a current of electrons lose energy when passing through a conductor? Consider the view an electron has as it moves between the fixed nuclei of the metallic conductor.

The electron has to negotiate the rapidly vibrating nuclei or positive ions in the conductor. Every time the electron collides with one of these ions it loses some of its energy. This energy goes into increasing the vibrational energy of the solid conductor. The temperature of the conductor rises as a result.
Figure 3.2.3 (3) Electrons have to pass through vibrating metal ions in the conductor.

Factors that influence resistance R of a conductor.

The resistance of an object depends upon the type of material from which it is made, the shape of the object and its temperature.

The number of collisions will also depend on the type of material. If the atoms and ions are closely packed, there will be more frequent collisions, and a high resistance will result. The amount of energy lost by the electron in a single collision will also depend on the type of material in the conductor. The more massive the atoms and ions, the more energy lost by the electron in the collision.

The shape is also important. A wire with a small cross-sectional area restricts the flow of charge through it.

The number of collisions suffered by an electron will increase as we increase the length of the conductor. Therefore the resistance also increases with length

In most Ohmic conductors, the resistance increases with temperature. At low temper¬atures the ions only vibrate slightly and hence electrons moving in the ‘channels’ between ions in the lattice will travel relatively large distances before colliding with an ion. At high temperatures the ions vibrate more energetically and occupy more space, which results in more frequent collisions with the conducting electrons. This reduces the average distance between collisions, and increases the resistance because the moving electrons transfer more of their energy (per unit length of wire) to the ions in the wire.
Non Omhic conductor

Conductors for which the voltage is not proportional to the current are called non Ohmic conductors. We can still define the resistance R of non Ohmic conductor for a particular voltage. The resistance of a non Ohmic conductor is not constant and is defined as the gradient of the tangent of the curve representing voltage versus current.
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