1. What is the resistivity of a wire?
2. According to Kirchhoff's first law, i.e., ΣI = 0 at a junction, what conservation principle does it deal with?
3. Why is constantan wire used for making standard resistance?
4. A large number of free electrons are present in metals. Why is there no current in the absence of an electric field?
Answer (2)
The resistivity of a wire measures its opposition to electric current, and Kirchhoff's first law relates to the conservation of electric charge. Constantan wire is preferred for standard resistance due to its stable resistivity, and current requires an electric field to enable the movement of free electrons in a metal. Without an electric field, free electrons move randomly, resulting in no current flow.
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What is the resistivity of a wire?
Resistivity is a property of a material that quantifies how strongly it resists or conducts electric current. It is denoted by the symbol ρ (rho) and is measured in ohm-meters ( Ω ⋅ m ). The resistivity of a wire is determined by the material of which the wire is made, its cross-sectional area, and its temperature. The formula to calculate resistance R is given by:
R = ρ A L
where L is the length of the wire and A is the cross-sectional area.
According to Kirchhoff's first law, i.e., Σ I = 0 at a junction, what conservation principle does it deal with?
Kirchhoff's first law, also known as the current law or junction rule, deals with the conservation of electric charge. It states that the total current entering a junction must equal the total current leaving the junction. This is a consequence of the conservation of charge, meaning that charge cannot be created or destroyed in an isolated system.
Why is constantan wire used for making standard resistance?
Constantan wire is used for making standard resistances because it has a relatively low and stable resistivity that does not change much with temperature variations. This stability makes it ideal for creating accurate and reliable resistors that maintain constant resistance over a range of temperatures, ensuring consistent performance in electrical circuits.
A large number of free electrons are present in metals. Why is there no current in the absence of an electric field?
In metals, free electrons are indeed present and move randomly at thermal equilibrium. However, in the absence of an electric field, these free electrons move in a random manner, resulting in no net flow of charge. For an electric current to occur, there must be a directed movement of electrons, which is typically achieved by applying an electric field that exerts force on the electrons, causing them to drift and create an electric current.
