what is resistance? unit, types, affecting factor top 10 most useful important facts

Introduction-

what is resistance?

Imagine you’re trying to walk through a crowded room. The more people in your way, the harder it becomes to move forward. In the same way, when electricity flows through a material, tiny particles called electrons are trying to move forward. But they don’t get a clear path. The material they’re moving through has its own atoms and molecules that get in the way. This opposition to the flow of electrons is called resistance.

So, in simple words:
“Resistance is the force that tries to slow down or stop the flow of electric current”.

The property of a substance due to which it opposes the flow of electric current flowing through it is called resistance. And the piece of substance that performs this function is called a resistor.

what is the unit of resistance?

Resistance is something that opposes the flow of electric current in a material. It’s like a roadblock that slows down the movement of electricity.

The symbol for resistance is ‘R’, and the unit of resistance is the ohm.

There is another unit, called the Abohm, used in the CGS system of measurement. One Abohm is equal to 10^{-9} ohms..

Ohm’s law gives a simple way to calculate resistance. It says: R=V/I

Where:

• R is the resistance,
• V is the voltage (or potential difference),
• I is the current.

To understand this better, let’s think about a simple example:

• If the voltage across a material is one volt, and a current of one ampere passes through it, the resistance of that material is one ohm.

R=1V/1I=1 Ohm

In a more accurate system, the value of one international ohm is slightly more than the regular ohm: it is 1.00049 absolute ohms.

To define the international ohm practically, scientists use a column of mercury to measure it. This is how we get a precise value for resistance in real-world measurements.

Ohm’s Law

A long time ago, a smart scientist from Germany named George Simon Ohm discovered something very important about electricity. He found a simple rule that tells us how voltage, current, and resistance are related in an electric circuit. This rule is called Ohm’s Law.

Let’s understand it step by step.

When electricity flows through a wire or any other material, three things matter:

• Voltage (V) – This is the force that pushes the electricity through. Think of it like water pressure.
• Current (I) – This is how much electricity is flowing. It’s like how much water is coming out of a tap.
• Resistance (R) – This is how much the wire or material tries to stop the electricity. It’s like a narrow pipe that makes it harder for water to flow.

Now, Ohm’s Law tells us this:

“If the temperature and other physical conditions don’t change, then the voltage (V) is always equal to the current (I) multiplied by the resistance (R).”

In simple words:

V = I × R

This means:

• If you know the voltage and resistance, you can find the current: I = V ÷ R
• If you know the current and resistance, you can find the voltage: V = I × R
• If you know the voltage and current, you can find the resistance: R = V ÷ I

Here’s an easy example:

If you double the voltage, the current also doubles. But the ratio between voltage and current stays the same. That’s the resistance, and it doesn’t change unless the wire gets hotter or something else changes.

If you draw a graph showing voltage on one side and current on the other, the line goes straight up from zero. This straight line shows that the relationship is steady and simple.

And finally, remember this:

• Voltage is measured in volts (V)
• Current is measured in amperes (A)
• Resistance is measured in ohms (Ω)

Properties of Resistor-

A resistor should have the following properties-

1. Should be cheap and easily available.

2. The wattage of the resistor should be high, the resistor which has a smaller diameter has a lower wattage. 3. Should not be affected by temperature. (Hence the value of temperature coefficient should be minimum) Example- Magnin. Whose temperature coefficient is almost zero (.000002 per degree centigrade), due to this reason it is not affected by temperature.)

Types of Resistor-

There are mainly two types of resistors-

1. Carbon Resistor
2. Wire wound resistors

Carbon resistors-

• This type of resistor is made by combining fine powders of carbon and graphite with a non-conductive bond.
• The diameter of these types of resistors is small, due to which their wattage ranges from 1/8 watt to 2 watts.
• These are used in electronic devices like radio, mobile, television etc.
• There are two types of carbon resistors-

a. Fixed value carbon resistor

b. Converted value carbon resistor

Fixed value carbon resistor

• The value of this type of resistor remains fixed, But it cannot be changed later.

• Their wattage value Ranges from 1/8 watts to 2 watts.

Note: The connecting lead of the resistor is made of tin coated copper.

Converted value carbon resistor

• Its value can be changed later.

• The carbon powder is molded into a crescent shaped strip using a bonding strip and it contains a connecting wire through which the resistance value of the resistor is later changed.

• Their value ranges from 1000 to 5 MM.

• Their wattage ranges from 0.0500 watts to 0.25 watts.

Wire wound resistors-

• This type of resistor is made by wrapping wire around a rod or insulating core.

• Here the core is usually made of porcelain, bakelite, press bond paper or ceramic.

• The wire of this type of resistors is made of manganin, nichrome or eureka (nickel 60% and copper 40% alloy wire).

• Their wattage ranges from 2W to 50W.

• Their value ranges from 0.1 to 50kΩ.

Note- Here the melting point of the coated wire should be high. That is, tungsten metal wire can also be used here.

These are of two types-

a. Fixed value wire wound resistor

b. Converted value wire wound resistor

Fixed value wire wound resistor

• Their value remains fixed. That is, it cannot be changed later.

• Wire wound resistance is made of Eureka. It is made of copper and nickel in the ratio of 55:45 respectively.

• Their value ranges from 0.1 to 50kΩ.

• Their wattage is up to 50W, but for industries resistors of higher capacity are also used.

converted wire wound resistor

• The resistance value of this type of resistor can be changed/varied later.

• Their shape is generally moon shaped.

• These are used as regulators.

• Their wattage is up to 50W.

• The value of their resistance ranges from 5 Ω to 5kΩ.

what is specific resistance?

Other types of resistors are as follows-

Thermistor-

• Thermal+Resistor means it is a resistor dependent on temperature.

• These are made from a mixture of metal oxides, nickel, cobalt, copper, uranium and manganin.

• The resistance value of the thermistor decreases as the temperature increases, i.e., it is an NTC type resistance.

• Their resistance is low and wattage is also low.

• These are used in electronics work.

Voltage Dependent Register / Varistor-

• The value of resistance of this type of resistor depends on the voltage.

• As the voltage value is high, the resistance value is low.

• Similarly, as the value of voltage decreases, the value of resistance increases.

• This type of resistors are used in television and power circuits.

These are of two types-

Symmetrical varistor-

• This type of resistor is made from carbide powder and ceramic binder material.

Asymmetrical Varistor-

• This type of resistor is made from semiconductor materials.

Light Dependent Register-

• The value of resistance of this type of resistor depends on light.

• The temperature coefficient of LDR is negative. That is, when the light level is high, the resistance level is low. Similarly, when the light level is low, the resistance level is high.

• It is made from selenium, cadmium sulphide, cadmium selenide and lead sulphide.

• These are used in light controlled circuits. Such as in street lights and lamps.

Metal film resistors-

• It is similar to a carbon resistor but instead of carbon, it has a film of metal oxide, nickel chromium.

• These are used in oscillators.

• These types of resistors are very cheap and easy to operate.

rheostat-

• The resistance value of this type of resistor can be decreased or increased more easily.

• These are used in laboratories.

• Their wattage is high.

Potentiometer-

• It has 3 terminals.

• It is a modified resistor of carbon type resistor.

• It is used for volume and tone control in radio receivers.

• Its resistance value is up to 1000 Ohms.

Factors Affecting Resistance-

We know that-

R=Pl/ A

where- p = Specific resistance (Ohm meter) l = Length (meter) A = Transverse area (square meter)

Specific resistance-

• The resistance of a conductor having one unit length and one square unit cross-sectional area is called specific resistance or resistivity.

• It is expressed p(phai)

• Resistivity depends on the nature of the substance and its temperature.

• now p= RxA/L ohm P = Ohm-meter (unit)

• The value of resistance is proportional to the length of the conductor wire.

Rocl

• The value of resistance is inversely proportional to the cross-sectional area of ​​the conductor wire.

Roc 1/a

• The resistance of a conductor also depends on the resistivity of the material.

Temperature Coefficient –

Effect of temperature on resistance-

The value of resistance changes when the temperature increases or decreases. Which we can know from the relation given below.

Case 1-

Calculate resistance at unknown temperature (T)-

R₁ = R [1+ a(T₂-T₁)]

Where R₁ = Resistance at T₂°C R = Resistance at T₁°C (T₂-T₁) = Change in temperature

a(alfa) = temperature coefficient of resistance (per °C)

Situation 2-

Suppose The Temperature Coefficient (A) Is To Be Found At Some Other Temperature And The Initial Temperature Coefficient Is (a0). In that case, the unknown temperature coefficient can be found by the following formula.

Case 3-

If the resistance at two unknown temperatures (R₁₂ and R₁₁) is known If the resistance is to be determined and the temperature coefficient (0) is known, then the other can be determined by the following formula if the resistance is available at one temperature.

Positive temperature coefficient resistor (PTC)-

• In this type of resistor, due to positive temperature coefficient, the value of resistance increases with increase in temperature and the resistance decreases with decrease in temperature.

• This type of effect occurs in metals like copper, silver, aluminium, platinum etc.

• Example- Sensor

Negative temperature coefficient resistor (NTC)-

• This type of resistor has a negative temperature coefficient. That is, the value of resistance decreases as the temperature increases.

This type of effect occurs in insulators and semiconductors.

• Example- Thermistor

Color Code-

• The size of carbon resistors is so small that color coding is preferred over printing the resistance value on it so that it is more convenient to display the value.

• Apart from this, if mixed resistors of many values ​​are filled in a single box, then it is convenient to express the resistance of the required value.

Methods of Color Marking-

• There are two popular methods of marking the value of resistor with different colors-

(1) Band Type

(2) Body Type

Band Type

• In this method, generally four bands or rings of different colours are marked on the body of the resistor.

• The colour of the first stripe represents the first digit of the resistance, the colour of the second stripe represents the second digit, the colour of the third stripe represents the multiplier and the fourth stripe represents the tolerance.

• Apart from this, two other types of bands are also used. These are classified into five band and six band categories. These are mentioned below.

note point-

1. In band type colour coding the first band cannot be silver, gold and black.
2. In band type colour coding the reading is always from left to right.

Body Type-

• In this method the entire body of the resistor is painted with one color, then one end is painted with another color and a circular and a rectangular dot of different colors are marked on the body.

• Example- Determine the resistance of a given resistor with the given color sequence (red, green, red, gold).

Various Combinations of Resistor-

The following are the combinations of resistors:

combination of resistances

series connection parallel connection mix connection

series connection

• A combination of two or more resistors, in which the value of current flowing through each resistance is the same, is called series combination.

• The value of total potential difference in a series combination is equal to the algebraic sum of the voltage drop across each resistance.

• Hence equivalent potential difference (V₁)

V₁ = V1 + V2 + V3

• According to Ohm’s law, the potential difference generated across the ends of a resistor is equal to the product of the current flowing through it and its resistance (I.R).

• the total resistance of the circuit is equal to the sum of the different resistance values.

note – If resistors of the same value are connected in series, the equivalent resistance from R₁ = n

Parallel Connection-

• A combination of two or more resistors, such that the potential difference across each resistor is the same, is called parallel combination.

• In this combination, the value of current is not the same. That is, the value of total current is equal to the algebraic sum of the current flowing in each resistance

• If “n” resistors are connected in parallel then the value of equivalent resistance (R₁) is-

R₁=r/n

• The equivalent resistance of a parallel combination is less than the lowest resistance of the combination.

Mix Connection:-

• Apart from series and parallel combinations, another combination which is made by combining the above two combinations is called mixed combination.

• Mixed combination is explained with the help of example below.

Classification of Resistance

Classification of resistance is generally of three types-

Low resistance-

• Those resistances whose value is less than 12 ohms fall in the low resistance category.

Example- resistance of armature winding

Medium resistance-

• Those resistances whose value ranges from 12 to 100 KΩ come under the category of medium resistance.

Example- bulb filament, heater, cathode (CRO)

High resistance-

Those resistances whose value is more than 100 KM come under the category of high resistance.

Example- insulation and earth resistance

Measurement of Unknown Resistor-

Using a Digital Multimeter (DMM):

• Set the multimeter to the resistance (Ω) mode.

• Disconnect the resistor from any circuit to avoid parallel paths or interference.

• Connect the multimeter probes across the resistor terminals.

• Read the resistance value directly from the display

Wheatstone Bridge Method

• A Wheatstone bridge is a precise method to measure an unknown resistor, especially for low resistance values.

• If the value of current in the glevanometer is zero, then the bridge will be in equilibrium position and in equilibrium position-

• The product of resistance of opposite sides is equal to each other. PS = RQ

Advantages:

• High accuracy
• Suitable for laboratory use

Disadvantages:

• Requires careful balancing
• Not suitable for rapid measurements

exam useful important facts

• Resistance is a bilateral and passive component.

• Components that obey Ohm’s law are curved linearly.

• One international ohm is defined by a column of mercury and its value is 1.00049 ohms.

• The resistance of a short circuit is zero while the resistance of an open circuit is infinite.

• The normal resistance of the human body is 10000 whereas in dry state this value ranges from 70 K ohm to 100 KΩ.

• The unit of specific resistance is ohm-meter.

• Resistors made of graphite are called carbon resistors.

• Potentiometer, thermistor and rheostat are called variable resistances.

• The full form of “LDR” is Light Dependent Resistor.

• This is a heat sensitive resistance.

• The full form of “PTC” is Positive Temperature Coefficient.

• Eureka resistance is used in froth regulator|
  
  
  

calculation

we believe in strong foundational knowledge. To understand how electricity works, we must ask: What is resistance? It’s the opposition offered by a material to the flow of electric current. But more specifically, what is electrical resistance? It’s defined as the ratio of voltage (V) across a conductor to the current (I) flowing through it. That is:

R = V / I

Where R is resistance in ohms (Ω), V is voltage in volts, and I is current in amperes. Now, As noted, it is measured in ohms (Ω). But another important aspect is specific resistance, also known as resistivity (ρ), which depends on the material and is calculated by:

ρ = R × (A / L)

Where A is the cross-sectional area and L is the length of the conductor. So, again, what is resistance? It helps us design circuits efficiently. What is electrical resistance? It’s critical to understand power loss in transmission lines. Every Kay World student must know: what is the unit of resistance? Ohm, derived from Georg Simon Ohm’s work. And to dive deeper, what is specific resistance? It varies between materials like copper and rubber. In your syllabus at Kay World, you’ll find the question: what is resistance class 10?—it’s all about introducing this concept clearly.

Let’s calculate! Suppose a wire has a voltage of 12V and a current of 2A. Then:

R = V/I = 12/2 = 6Ω

Students might ask again, what is resistance? What if we change the material? Then we deal with resistivity. So, what is specific resistance? It’s the property of the material itself. At Kay World, every unit begins by asking, what is resistance? what is electrical resistance? what is the unit of resistance? what is specific resistance? what is resistance class 10?—because repetition builds mastery.

FAQ

read more-