1. A copper wire is stretched so that its length is increased by 0.1 percent. The percentage change in its resistance is
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2. The resistance of wire of uniform diameter d and length L is R. The resistance of another wire of same material but diameter 2d and length 4 L will be
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3. A wire has a resistance of 10 ohm. It is stretched by one-tenth of its original length. Then its resistance will be
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4. Eureka has temperature co-efficient of resistance
Explain:- Eureka, also known as Constantan, is a copper-nickel alloy that has a very low temperature coefficient of resistance. This means that its resistance changes very little with temperature, making it suitable for applications where a constant resistance is required, such as in electric heating elements and strain gauges.The composition of Eureka/Constantan is typically 55% copper and 45% nickel, and it has a negligible temperature coefficient of resistance
5. A primary cell has an e.m.f. of 1.5 V. When short-circuited, it gives a current of 3A. The internal resistance of the cell is
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6. An electric fan and a heater are marked 100 W, 220 V and 1000 W, 220 V respectively. The resistance of heater is
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7. Two resistances are joined in parallel whose resultant resistance is 6/5 ohm. One of the resistance wire is broken and the effective resistance becomes 2 ohms, then the resistance of the wire that got broken is
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8. A linear circuit is one whose parameters (e.g. resistance etc.)
Explain:- A linear circuit is an electronic circuit that follows the principle of superposition, meaning that the output of the circuit is directly proportional to the input. The direction of the current is independent of the behavior of the element. Resistors, inductors, and capacitors are examples of linear circuit parameters. Linear circuits are important because they can amplify and process electronic signals without distortion. An example of an electronic device that uses linear circuits is a sound system. In contrast, a nonlinear circuit is an electric circuit whose parameters are varied with respect to current and voltage. In other words, an electric circuit in which circuit parameters (resistance, inductance, capacitance, waveform, frequency, etc.) are not constant is known as a nonlinear circuit. Examples of nonlinear circuits include diodes, transistors, and MOSFETs.
9. Find Thevenin equivalent circuit to the left of the terminal X-Y in fig.
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10. What percentage of the maximum power is delivered to a load if load resistance is 10 times greater than the Thevenin resistance of the source to which it is connected ?
Explain:- The maximum power transfer theorem states that the power delivered to a load is maximized when the load resistance is equal to the Thevenin resistance of the source to which it is connected. In other words, the load resistance should be equal to the resistance of the circuit when all voltage sources are replaced by open circuits and all current sources are replaced by short circuits. This theorem is applicable to linear, bilateral DC networks.To calculate the maximum power transfer, you can use the following formula: pmax=V2th/4Rth
11. How much electrical energy in kWh is consumed in operating ten 50 W bulbs for 10 hours in a day in a month of 30 days ?
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12. You are given three bulbs of 25 W, 40 W and 60 W. Which of them has the lowest resistance ?
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13. A fuse is made of
Explain:- A fuse is an electrical safety device that provides overcurrent protection for an electrical circuit. The fuse element is made of various metals, such as zinc, copper, silver, aluminum, or alloys among these or other materials, to provide stable and predictable characteristics. The fuse wire is typically made of an alloy of tin and lead, which has a low melting point and high resistance. The fuse element is arranged in series to carry all the charge passing through the protected circuit, and its resistance generates heat due to the current flow. The size and construction of the element are determined so that the heat produced for a given current flow will cause the fuse to melt quickly when a small excess current flows.
14. The force between two electrons separated by a distance r varies as
Explain:- According to Coulomb's law, the force between two electrons separated by a distance r varies inversely as the square of the distance between them. The mathematical expression for Coulomb's law is F = K(q1q2/r2), where F is the force, q1 and q2 are the charges of the two electrons, r is the distance between them, and K is Coulomb's constant
15. When relative permittivity of the medium is increased, the force between two charges placed at a given distance apart
Explain:- When the relative permittivity of the medium is increased, the force between two charges placed at a given distance apart decreases. Relative permittivity, also known as the dielectric constant, is the factor by which the electric field between the charges is decreased relative to vacuum. It is related to the capacitance of a capacitor using that material as a dielectric, compared to a similar capacitor with vacuum as its dielectric. The mathematical relationship between the force, relative permittivity, and the distance between the charges is not a simple direct proportionality, but an increase in relative permittivity does lead to a decrease in the force between the charges.
16. The potential at a point due to charge is 9 V. If the distance is increased three times, the potential at a point will be
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17. A soap bubble is given a negative charge. Its radius
Explain:- When a soap bubble is given a negative charge, its radius increases. This is because the charges on the surface of the bubble repel each other, causing the bubble to expand and increase its radius. The charge will be distributed uniformly over the surface of the bubble by symmetry, and the repulsion of the charges will result in a new, larger radius of equilibrium.
18. The capacitance of a parallel-plate capacitor depends upon
Explain:- The capacitance of a parallel-plate capacitor depends on the area of the plates and the distance between them. The capacitance (C) is given by the formula C = Kε0A/d, where ε0 is the permittivity of free space, A is the area of the plates, and d is the separation between the plates. This means that the capacitance is directly proportional to the area of the plates and inversely proportional to the separation between them. Additionally, the capacitance can be affected by the type of dielectric material between the plates, as indicated by the relative permittivity (k) in the formula.
ϵo is the permittivity of space (8.854 × 10−12 F/m)
k is the relative permittivity of dielectric material
d is the separation between the plates
A is the area of plates
19. The capacitor of capacitances C1 and C2 are connected in parallel. A charge Q given to them is shared. The ratio of charges Q1/Q2 is
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20. A capacitor of 20 microF charged to 500 V is connected in parallel with another capacitor of 10 microF capacitance and charged to 200 V. The common potential is
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21. Which of the following does not change when glass slab is introduced between the plates of charged parallel plate capacitor ?
Explain:- When a glass slab is introduced between the plates of a charged parallel plate capacitor, the quantity that does not change is the charge on the plates. The introduction of the glass slab increases the capacitance of the capacitor, which in turn decreases the potential difference between the plates. However, the charge on the plates remains the same because the charge is conserved.
22. The magnetic material used in permanent magnets is
Explain:- The magnetic material used in permanent magnets is typically made from ferromagnetic materials, which include iron, nickel, and cobalt, as well as some rare earth metals. These materials exhibit strong magnetic properties and are used to create permanent magnets with varying levels of strength and resistance to demagnetization. Some common types of permanent magnets include:
1.Alnico magnets: Composed of aluminum, nickel, and cobalt, these magnets have been popular since the 1930s and are used primarily in technical applications.
2.Samarium Cobalt magnets: A class of rare-earth magnet materials introduced in the early 1970s, these magnets have high magnetic properties and are used in applications that require elevated temperatures.
3.Neodymium magnets: The strongest permanent magnets, neodymium magnets are made from an alloy of iron and boron. They are known for their high magnetic strength and are commonly used in various industrial and non-technical applications.
4.Ceramic (Ferrite) magnets: These magnets are relatively hard, brittle, and dark gray in color. They are popular for many consumer applications due to their relatively high magnetic strength and good resistance to demagnetization.
Permanent magnets are made from special alloys (ferromagnetic materials) such as iron, nickel, and cobalt, as well as several alloys of rare-earth metals and minerals. The choice of material depends on the specific application requirements, such as temperature resistance, magnetic strength, and corrosion resistance.
23. Magnetic flux density is a
Explain:- Magnetic flux density, symbolized by B, is a measure of the strength of a magnetic field. It is defined as the force per unit of sensitive element, which in this case is a current. In physics, it is a vector field denoted by B and has units of tesla (T) or weber per square meter (Wb/m2). The magnetic flux density is an indirect measure of the strength of a magnetic field and describes the density of the magnetic flux through a surface.
24. Magnetic flux passes more readily through
Explain:- The magnetic field lines prefer to pass through iron than air because the permeability of iron is much larger than air.
25. Iron is ferromagnetic
Explain:- Metals have a transition temperature, called the Curie point (Tc), at which the magnetic properties are drastically changed. For iron, this temperature is 770 C, above which Fe begins to transform from BCC to FCC. The low-temperature BCC iron is ferromagnetic. When an external (in this case from the house magnet) magnetic field is applied to the iron, it produces a spontaneous alignment of the spins of electrons in the valence bands, which in turn produce a net magnetic moment, M, inside the iron. Below the Curie point, this magnetic moment in the material is self-stabilizing and it persists even when the external magnetic field is removed.
26. When the relative permeability of a material is slightly more than 1, it is called a
Explain:- When the relative permeability of a material is slightly more than 1, it is called a paramagnetic material. Paramagnetic materials have a relative permeability between 1 and 100, and their magnetic susceptibility is positive. In contrast, diamagnetic materials have a constant relative permeability slightly less than 1, and their magnetic susceptibility is negative. The permeability of a material is a measure of its ability to support the formation of magnetic fields.
27. The reluctance of a magnetic circuit varies as ________
Explain:- The reluctance of a magnetic circuit varies as the length divided by the area, or R ∝ l/A.Reluctance is a scalar quantity that is directly proportional to the length of the magnetic circuit and inversely proportional to the area of the cross-section of the magnetic path. It is also inversely proportional to the magnetic field strength (H) and the permeability (μ) of the material of the magnetic circuit.