A coil is formed by winding 250turns of insulated 16-gauge copper wire (diameter = 1.3 mm) in a single layer on a cylindrical form of radius 12cm. What is the resistance of the coil? Neglect the thickness of the insulation. (Use Table 26-1.)
The resistance of the coil is 2.4.
The voltage is directly proportional to the current and the constant of proportionality is called Resistance. This is called Ohm’s law.
We can find the total length of the coil by using the radius of the coil. We can also find the area of the cross-section of the wire from its diameter. Then, by using these values in the formula for resistance, we can find the resistance of the copper coil.
The resistance of a wire due, …(i)
Here, R is resistance, p is resistivity, L is length, A is the area of cross-section.
The circumference of the circle, …(ii)
is circumference, is the radius of the circle.
The cross-sectional area of a circle, …(iii)
Length of one turn of the coil can be given using the circumference of the circle.
So, the length of 250 turns of the coil using equation (ii) would be,
Similarly, the cross sectional area of the wire is given using equation (iii) as follows:
Resistivity of copper is
Now, using these above values in equation (i); the resistance of the copper coil can be calculated as follows:
Therefore, the resistance of the copper coil is .
A current is established in a gas discharge tube when a sufficiently high potential difference is applied across the two electrodes in the tube. The gas ionizes; electrons move toward the positive terminal and singly charged positive ions toward the negative terminal.(a)What is the current in a hydrogen discharge tube in which electrons and localid="1661417709864" protons move past a cross-sectional area of the tube each second? (b) Is the direction of the current density toward or away from the negative terminal?
Swimming during a storm. Figure shows a swimmer at distance D = 35.0m from a lightning strike to the water, with current l = 78 kA. The water has resistivity , the width of the swimmer along a radial line from the strike is 0.70m , and his resistance across that width is . Assume that the current spreads through the water over a hemisphere centered on the strike point. What is the current through the swimmer?
Earth’s lower atmosphere contains negative and positive ions that are produced by radioactive elements in the soil and cosmic rays from space. In a certain region, the atmospheric electric field strength is 120V/m and the field is directed vertically down. This field causes singly charged positive ions, at a density of 620cm-3 , to drift downward and singly charged negative ions, at a density of 550cm-3 , to drift upward (Figure). The measured conductivity of the air in that region is . Calculate (a) the magnitude of the current density and (b) the ion drift speed, assumed to be the same for positive and negative ions.
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