Table of Contents
The resistivity of metals increase with increase of temperature. The resistivity of semiconductors and insulators decrease with increase in temperature. Means the semiconductors and insulators are having negative temperature coefficient of resistance.
What factors affect resistivity?
The resistivity of a material depends on its nature and the temperature of the conductor, but not on its shape and size. A good conductor has less resistivity, whereas a bad conductor or insulator has high resistivity. The resistivity of semi-conductors lies between that of conductors and insulators.
What are the factors affecting the resistivity of a conductor and how?
The resistance of the conductor depends on the following factors:
- The temperature of the conductor.
- The cross-sectional area of the conductor.
- Length of the conductor.
- Nature of the material of the conductor.
Does resistivity depend on length?
When current flows through a component, the resistance depends on the geometry (length and cross-sectional area) of the component and a property of the material (resistivity). The resistance of a wire is proportional to its length and inversely proportional to its cross sectional area.
Does resistivity change with temperature?
The more these atoms and molecules bounce around, the harder it is for the electrons to get by. Thus, resistance generally increases with temperature. For small temperature changes the resistivity varies linearly with temperature: r = ro (1 + a DT), where a is the temperature coefficient of resistivity.
How can we reduce resistivity?
When the grounding electrode does not achieve a low enough resistance, another option is to reduce the resistivity of the soil.Some methods to reduce the soil resistivity include:
- Water retention.
- Chemical salts.
- Bentonite.
- Chemical-type electrodes.
- Ground enhancement materials.
Is resistivity directly proportional to resistance?
Resistivity ρ is an intrinsic property of a material and directly proportional to the total resistance R, an extrinsic quantity that depends on the length and cross-sectional area of a resistor. The resistivity of different materials varies by an enormous amount.
Why does resistivity of a metal increases with temperature?
As electrons move through a metal conductor, some collide with atoms, other electrons or impurities. These collisions cause resistance and generate heat. Heating the metal conductor causes atoms to vibrate more, which in turn makes it more difficult for the electrons to flow, increasing resistance.
What happens to resistivity when length is doubled?
the resistance of a conductor is directly proportional to its length. so if length is increased then resistivity increases ande vice versa. so if length is doubled resistance will also get doubled i.e resistance is 4 times that of original resistance.
What are the two factors that influence resistance?
There are several factors that affect the resistance of a conductor;
- material, eg copper, has lower resistance than steel.
- length – longer wires have greater resistance.
- thickness – smaller diameter wires have greater resistance.
- temperature – heating a wire increases its resistance.
What determines the resistivity of a material?
The electrical resistivity (ρ) of a solid object is determined by passing an electric current through a specimen and then measuring the resultant voltage drop over a certain length. It is expressed by the relationship between the electrical field inside the material and the flowing electric current.
How can we make earthing effective?
Use two earth leads with each earth plate (in case of two earth plates) and tight them. To protect the joints from corrosion, put grease around it. Collect all the wires in a metallic pipe from the earth electrode(s). Make sure the pipe is 1ft (30cm) above the surface of the ground.
What is the resistance of steel?
Table of Resistivity and Conductivity at 20°C
| Material | ρ (Ω•m) at 20 °C Resistivity | σ (S/m) at 20 °C Conductivity |
|---|---|---|
| Carbon steel | (10 10) | 1.43×10 −7 |
| Lead | 2.2×10 −7 | 4.55×10 6 |
| Titanium | 4.20×10 −7 | 2.38×10 6 |
| Grain oriented electrical steel | 4.60×10 −7 | 2.17×10 6 |
What causes resistance?
An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance.
Does resistivity depend on length and area?
The resistivity of a material depends on its nature and the temperature of the conductor, but not on its shape and size.
What are the 4 factors that affect resistance?
There are 4 different factors which affect resistance:
- The type of material of which the resistor is made.
- The length of the resistor.
- The thickness of the resistor.
- The temperature of the conductor.
Which earthing is used in rocky soil?
Another alternative to going for an effective earthing system for rocky areas is to use a ground rod in the soil. But you need to keep it in mind that the ground rod must go down the lowermost frost depth. Using ground enhancement material can also help you get effective ground in rocky areas.
What increases the resistivity of a material?
The general rule is resistivity increases with increasing temperature in conductors and decreases with increasing temperature in insulators.
Why do metals have low resistance?
Answer:Conductors have number of free electrons in them hence they have low resistance. As number of electrons increases resistance of the matter decreases because number of electrons will decide flow of current or heat through it.
What are the 3 factors that affect resistance?
Resistance is the property of the material that restricts the flow of electrons. There are four factors affecting resistance which are Temperature, Length of wire, Area of the cross-section of the wire, and nature of the material.
What increases resistance in a wire?
Resistance increases with the temperature of the wire. The hotter wire has a larger resistance because of increased vibration of the atomic lattice. When a material gets hotter the atoms in the lattice vibrate more.
Why does resistivity decrease with temperature?
When the temperature in increased the forbidden gap between the two bands becomes very less and the electrons move from the valence band to the conduction band. Thus when the temperature is increased in a semiconductor, the density of the charge carriers also increases and the resistivity decreases.
Which will have more electrical resistivity a piece of paper or a metal?
Answer. Silver has the highest electrical conductivity of all metals.
What is called specific resistance?
Specific resistance is defined as the resistance offered per unit length and unit cross-sectional area when a known amount of voltage is applied.
What metal has the highest resistivity?
The various high resistivity materials (including alloys) are described below:
- Tungsten: (i) Hard metal.
- Carbon: (i) ρ = 1000 to 7000 μ ohm cm, α = – 0.0002 to – 0.0008.
- Nichrome or Brightray B: Composition:
- Nichrome V or Brightray C:
- Manganin:
- Constantan or Eureka:
- German Silver or Nickel Silver or Electrum:
- Nirosta:
How can we improve earthing?
3 good ways to improve earth electrode resistance
- Lengthen the earth electrode in the earth.
- Use multiple rods.
- Treat the soil.
