For the same wire,
(A) resistance is higher in summer
(B) resistance is higher in winter (c) resistance is same in summer and winter (d)non of these
Answers
Answer:
1. Tungsten:
(i) Hard metal.
(ii) Resistivity twice that of aluminium.
ADVERTISEMENTS:
(iii) Can be drawn into very thin wires (for making filaments). The thinner the tungsten wire, the greater is its tensile strength.
(iv) In the atmosphere or inert gas (Nitrogen, Argon etc.) or in vacuum, tungsten can be readily worked at temperatures like 2000°C and even higher.
(v) Oxidises very quickly in the presence of oxygen even at temperature of a few hundred degree centigrade.
Uses:
ADVERTISEMENTS:
I. This material is used in electronic and vacuum engineering. Used as filament in lamps, electrodes, heaters, springs etc. It is also used in electron, X-ray and other kinds of tubes.
II. The tungsten filament is made in straight, coiled or coiled-coil form. The straight filament has tendency to sag if the lamp is operated in horizontal position. Coiled filament concentrates the light. Coiled-coil filament is used when an extremely concentrated light source is needed like in projectors.
III. The great hardness and high boiling and melting point of tungsten coupled with its resistance to abrasion establish this metal as an outstanding material for electrical contacts in certain applications. It is extremely resistant to the destructive acting forces.
Properties of Tungsten Conductor:
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(i) Specific weight … 20 g/cm3
(ii) Melting point … 3410°C
(iii) Boiling point … 5900°C
(iv) Thermal coefficient of expansion … 4.4 x 10-9 per degree
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(v) Resistivity … ρ = 0.055 Ω mm2/m
(vi) Temperature coefficient of resistance … α = 0.005
The tungsten is produced by very complicated processes from rare ores or from a tungstic acid.
2. Carbon:
(i) ρ = 1000 to 7000 μ ohm cm, α = – 0.0002 to – 0.0008
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(ii) Melting point = 3500°C
(iii) Density 1.7 to 3.5.
Uses:
1. Carbon is used in automatic voltage regulators for making the pressure sensitive pile resistors.
2. It is used in the manufacture of welding electrodes, fixed and variable resistors for light current and contacts of certain classes of D.C. switch gear.
Carbon brushes reduce considerably the severity of sparking and rate of commutation wear in electrical machines.
3. Nichrome or Brightray B:
Composition:
Ni = 60%, Cr = 15%, Fe = 25%.
Properties:
(i) Resistivity … ρ = 1.10 μΩ cm
(ii) Temperature coefficient of resistance … α = 0.0002 per degree
(iii) Specific gravity … 8.24
(iv) Melting point … 1350°C
Uses:
It is used in making of tubular heaters and electric irons.
4. Nichrome V or Brightray C:
Composition:
Ni = 80%, Cr = 20%
Properties:
(i) Resistivity … ρ = 40 m ohm cm
(ii) Temperature coefficient of resistance … α = 0.0001 per degree
(iii) Specific gravity … 8.4
(iv) Melting point … 1400°C
(v) Possess high resistance to oxidation and temperature effects.
Uses:
It is employed in the making of heating elements and furnaces.
5. Manganin:
Composition:
Cu = 84%; Mn = 12%; Ni = 4%.
Properties:
(i) Resistivity … ρ = 44 μΩ cm
(ii) Temperature coefficient of resistance … α = ± 0.0015 per degree
(iii) Specific gravity … 8.19
(iv) Melting point … 1020°C.
Uses:
It is used in instrument shunts and standard resistance coils.
6. Constantan or Eureka:
Composition:
Ni = 40%; Cu = 60%.
Properties:
(i) Resistivity … ρ = 44 μΩ cm
(ii) Temperature coefficient of resistance … α = 0.00002 per degree
(iii) Specific weight … 8.9
(iv) Melting point … 1300°C
(v) Heat resisting properties – poor.
Uses:
It is used for making starters, field regulator resistances; wires for resistance boxes and thermocouples.
Answer:
For the same wire, (A) resistance is higher in summer.
Explanation:
- Resistance is defined as the measurement of the opposing which helps the current to flow in the electrical circuit.
- A German scientist by name Georg Simon Ohm studies about the relationship between the voltages, current and resistance
- The SI unit of Resistance is ohm.
- Ohm is defined as the when the transmission of the current of one ampere will be subjected to a potential difference of one volt.
Given that:
For the same wire,
To find:
The resistance =?
solution:
In the same wire, we have to consider that,
When the temperature tends to be increases, the resistances will also increase.
During the weather of both summer and winter.
The resistance will be greater than winter season.
Therefore, the resistance is higher in summer.
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