Unit of conductivity measures the frequency of passing of current or heat through any object. The standard measure for conductance is Siemens per meter or S/m. Anything which passes electricity through them is termed a conductor. The amount of electricity a material can carry is known as electrical conductivity.
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Keyterms: conductivity, conductor, electricity, conductance, siemens, electric field, electrical resistance, Electric current, electrical charge
Electrical Conductivity
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Electrical conductivity is a property of a material which is also known as specific conductance. Electric current is the number of electrical charges flowing through a particular area in a unit of time.
Electrical conductivity is expressed as the ratio of current density to the strength of the electric field. Its SI unit is siemens per meter (s/m) which is represented by e.
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Electrical Resistivity
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The opposite of electrical conductivity is electrical resistance. It is the estimation of the potential of the material to restrict the flow of current. The resistivity of a conductor depends on the area of the material, the nature of the material, and the length of the conductor.
Ωm is the SI unit of electrical resistivity.
- Resistivity and the resistance of material change with the temperature.
- Alloys are mostly used in electrical heating devices because the resistivity of an alloy is comparably higher than that of its constituent metals which is why it doesn't oxidize at high temperature.
- Metals have low resistivity which makes them good conductors of heat
- Insulators such as graphite, plastic, glass, rubber, etc Are higher in resistivity in comparison to metallic conductors.
- A semiconductor is a type of material whose resistivity is inversely proportional to the temperature. The impurities present affect the resistivity of a semiconductor.
Relativity of Different Materials
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| Material | Resistivity | |
|---|---|---|
| Conductor | silver Copper Aluminium Tungsten iron Lead Mercury | 1.59 x 10-8 1.68 x 10-8 2.65 x 10-8 5.6 x 10-8 9.71 x 10 -8 22 x 10-8 98 x 10-8 |
| Alloys | Constantan (cu+Ni) Manganin (Cu + Ni + Mn) Nichrome (Ni + Cr + Mn + Fe) | 49 x 10-8 48.2 x 10-8 100 x 10-8 |
| Insulators | Glass Hard Rubber | 1 – 10000 x 109 1-100 x 1013 |
Electrical Resistors
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Resistors are used to manage the flow of current in the circuit. It consists of several color codes. The different value of resistance is expressed by the different colors marked on the resistor.
Formula
- When materials have current density and a magnetic field,
ρ = E/J
Where, ρ = the resistivity of the material
E = the intensity of the magnetic field
J = the intensity of the current density
- Conductors with a regular cross-section and a regular flow of electric current. ,
Resistivity (ρ) = R A/l
R = electrical resistance of the regular cross-section
A = area of the cross-section
L = the length of the piece
V = W/Q
Where V = potential difference between two points in an electric circuit
W= work done
Q= charge
P = VI
Where,
P= electric power or the rate at which energy is consumed in the electric circuit
V= potential difference
I= current
- Joule’s law of heating
H= I2Rt
- Ohm’s law
V=IR
Where R = Resistance which is constant at a given temperature
- The relationship between electrical resistivity and electrical conductivity is expressed as
σ = 1/ρ
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Things to Remember based on Unit of Conductivity
- Electrical conductivity is a measurement of how an electrical current moves within a substance.
- A higher measurement of conductivity within a material represents a greater current density for applied potential difference.
- Electrical conductivity is important because high conductivity is required as a necessity in certain substances.
- Unit of conductivity in electricals is siemens per meter or S⋅m-1.
- The name siemens for unit of conductivity was introduced by the 14th General Conference on Weights and Measures as an SI-derived unit in 1971. It was named after Ernst Werner von Siemens.
- The dimension of resistivity is M1L3T-3A-2
- Factors that determine the relativity of the conductor are temperature and nature of the material
- Voltammeter is the device to measure the potential difference
- The rheostat is the device that is used to change the resistance in the circuit in an electric circuit
- Electric circuit Is the term given to a continuous and closed path of an electric current
Sample Questions based on Unit of Conductivity
Ques. A filament of an electric bulb draws 0.5A Current for 10 mins. Calculate the amount of electric charge that flows through the circuit. (2 Marks)
Ans. given, I = 0.5A, t= 10 mins or 600 sec
Q = It
= 0.5a x 600s
= 300c.
Ques. What is the power of the bulb which is connected to a 220V generator and having a flow of the current of 0.50A.? (2 Marks)
Ans. P = VI
= 220 V x 0.50A
= 110 J/S
=110W
Ques. A charge of 2C moves across two points of 12V potential difference. How much work has to be done? (2 Marks)
Ans. 2C amount of charge flows between two points at a potential difference of 12V. thus the amount of work done is:
W= VQ
= 12V x 2c
= 24J
Ques. What is the unit of conductivity of solution? (3 Marks)
Ans. Conductivity or specific conductance = conductance × cell constant
Cell constant = 1/A
Conductance = 1/resistance
∴ Conductivity = ohm−1 × cm/cm2
Units of conductance = ohm−1 cm−1
Ques. An electric refrigerator with 400W works for 8 hours per day. If it works for 30 days at rs 3.00 per kW h, find the cost of energy. (3 Marks)
Ans. the total energy used by the refrigerator in 30 days = 400W x 8.0 hours/day x 30days = 96000 Wh
= 96 kWh
The cost of energy used by the refrigerator for 30 days = 96kWh x rs 3.00 per kWh = rs 288
Ques. An electrical heater uses a current of 4A and has a potential difference between the terminals of 60V. if the potential difference is 120V, how much current will the heater consume? (3 Marks)
Ans. Potential difference (V) = 60V, current (I) = 4A
Applying Ohm’s law
R = V/I
= 60V/4A = 15Ω
When the potential difference is 120V
Current (I) = V/R = 120 V/12Ω = 8A
Thus, the current through the heater is 8 A when the potential difference is 120 V.
Ques. An electric lamp and a conductor of 20 Ω and 4 Ω respectively are connected to a battery of 6 V. calculate: (5 Marks)
(i) The total resistance of the circuit
(ii) The flow of current through the circuit
(iii) The potential difference between the conductor and the electric lamp
Ans. Resistance in the lamp (R1) = 20Ω
Resistance in the conductor (R2) = 4Ω
Total resistance = R1 + R2
R s = 20Ω + 4Ω = 24Ω
The total potential difference across the two terminals of the battery
V= 6V
Applying Ohm's law
I = V/R
= 6V/24Ω
= 0.25A
The potential difference across the electrical lamp
V1 = 20Ω x 0.25A
= 5V
The potential difference across the conductor
V2 = 4Ω x 0.25A
= 1V
Resistance (R) = V/I
= 6V/0.25A
= 24Ω
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