Resistors
How does a light bulb work?Inside the glass case of a light bulb, there is a tungsten rod, which glows when electric current passes through it. The glass case is filled with nitrogen or other non-flammable gas because tungsten burns if it contacts with oxygen. Tungsten rod is just a resistor.
What is a resistor?
A common resistor is shown in the Picture. Also note the symbol for the resistor. Although a tungsten rod is a resistor, the resistor used in electronics is of a different type. A resistor resists the flow of current. Physically, a resistor converts the electromagnetic energy into light or heat energy.
You can think of resistance as friction. Whenever you roll a ball on a path or on the floor, it encounters resistance from the path; that is expected. A copper wire, which conducts current, does have resistance, but when we say resistor placed in a circuit, we refer to a situation where a higher amount of resistance is provided for the current. It is like stick or rocks in the path of a ball that significantly resists the rolling of the ball.
Electromagnetic energy can be thought of as used to "drive the charges against the resisting force of electrical (or charge) "friction"".
The current flowing into the resistor and out of the resistor is same. Then what do you mean when you say the resistor resists the flow of current?
Consider the below cases. The second circuit has higher value resistor. The current flowing in entire circuit is much less due to higher resistance.
How does the electromagnetic energy is transformed into light or heat energy in a resistor?
I don't know the details.
Why is a resistor used?
Oftentimes, a certain device can only tolerate a certain range of current or we may want a certain voltage drop between two terminals. A resistor is useful in those situations.
What exactly is a resistor, physically?
Physically, the resistor is just a conductor or semi-conductor with high resistavity. It is just a piece of rod designed to provide specific resistance.
What do you mean by specific resistance?
The relationship between resistance, voltage and current is described by Ohms law.
What is the Ohms law?
The Ohms law states that V=IR, where V is voltage, I is current, R is resistor value or resistance. The unit of resistance is ohms.
Are there resistors for all values?
Technically yes. There are standard resistors produced by manufacturers and one can get any resistance by combining the standard resistors in series and parallel arrangements. There are also adjustable resistors.
What is a series arrangement of resistor?
Resistors placed side by side as in Figure is a series arrangement. The value of the resistor is sum value of the resistor value: Rt = R1 + R2
What is a parallel arrangement of resistors?
Resistors placed as shown in Figure are in a parallel arrangement.
The total value is 1/Rt=1/R1 + 1/R2; Rt = R1 R2 / (R1 + R2)
How do we measure the resistance of a resistor?
Resistance can be measured using a multi-meter or you can calculate it from the resistor code painted on it.
What is the resistor code?
The resistor code allows us to caculate the resistor values based on a colour code and a formula. The colour code is as follows:
R=(a x 10 + b)m + tolerance
|
a, b 0-black 1-brown 2-red 3-orange 4-yellow 5-green 6-blue 7-violet 8-gray 9-white |
Multiplier=m silver-0.01 gold-0.1 black-1 brown-10 red-100 orange-1K yellow-10K green-100K blue-1M violet-10M gray-100M |
Tolerance red-2% gold-5% silver-10% none-20% |