29. Sources of Magnetic Field

As you move a compass around a wire carrying current, what happens to the compass needle?

A 2.0-m-long, 1.0-mm-diameter wire has a variable resistivity given by where x is measured from one end of the wire. What is the current if this wire is connected to the terminals of a 9.0 V battery?

A circuit you're building needs an ammeter that goes from 0 mA to a full-scale reading of 50 mA. Unfortunately, the only ammeter in the storeroom goes from 0 μA to a full-scale reading of only 500 μA. Fortunately, you've just finished a physics class, and you realize that you can make this ammeter work by putting a resistor in parallel with it, as shown in FIGURE P28.56. You've measured that the resistance of the ammeter is 50.0 Ω, not the 0 Ω of an ideal ammeter. What is the effective resistance of your ammeter?

The current in a wire varies with time according to the relationship $I=55A-\left(0.65A/s^2\right)t^2$ . How many coulombs of charge pass a cross section of the wire in the time interval between $t=0$ and $t=8.0\text{ s}$?

The total amount of charge that has entered a wire at time t is given by the expression $Q=\left(20C\right)(1-e^{-\frac{t}{2.0s}})$, where t is in seconds and t≥0. What is the maximum value of the current?

The Hall voltage across a conductor in a 55 mT magnetic field is 1.9 μV. When used with the same current in a different magnetic field, the voltage across the conductor is 2.8 μV. What is the strength of the second field?

A proton moves along the x-axis with vₓ = 1.0 x 10⁷ m/s. As it passes the origin, what are the strength and direction of the magnetic field at the (x, y, z) positions (a) (1 cm, 0 cm, 0 cm), (b) (0 cm, 1 cm, 0 cm), and (c) (0 cm, -2 cm, 0 cm)?