Exam 25: Electric Current and Direct-Current Circuits

The current in a wire varies with time according to the relation where I is in amperes and t is in seconds.The number of coulombs that pass a cross section of the wire in the time interval between t = 0 and t = 1/20 s is

A 12-V battery has an internal resistance of 0.20 $\Omega$ .If the battery is being charged by a current of 30 A,the magnitude of the potential difference between its terminals is

Use the following figures to answer the next problem. -An uncharged capacitor and a resistor are connected in series to a battery as shown. If $\varepsilon$ = 15 V,C = 20 $\mu$ F,and R = 4.0 $\times$ 10⁵ $\Omega$ ,the maximum current in the circuit is approximately

You want to use a metal bar as a resistor.Its dimensions are 2 by 4 by 10 units.To get the smallest resistance from this bar,you should attach leads to the two opposite sides that have the dimensions of

A resistor of 2 $\Omega$ and another of 3 $\Omega$ are connected in parallel,and this combination is joined in series with a 4- $\Omega$ resistor across a battery.If the current in the 2- $\Omega$ resistor is 2.0 A,the potential drop across the 3- $\Omega$ resistor is

A capacitor,initially uncharged,is connected in series to a 10-k $\Omega$ resistor and a 9.0-V battery.What is the initial current in this circuit?

Consider a conductor for which Which of the following is an expression for $\rho$ ?

Given a sensitive galvanometer G and a collection of resistances of various values,a voltmeter can be constructed by

A 20- $\mu$ F capacitor is charged to 200 V and is then connected across a 1000- $\Omega$ resistor.What is the initial charge on the capacitor?

You want to determine the resistance R of a resistor by passing a current I through it,measuring this current with an ammeter connected in series with the resistor,measuring the voltage V across only the resistor with a voltmeter,and then dividing the voltage by the current to get the resistance.If the voltmeter has an internal resistance of 5.0 k $\Omega$ ,what is the percentage error (relative to the true value)in measuring a 1.0-k $\Omega$ resistance?

In a certain particle accelerator,a current of 800 $\mu$ A is carried by a 6.00-MeV proton beam that has a radius of 1.50 mm.The mass of a proton is 1.67 $\times$ 10^-27 kg.If the beam hits a target,how many protons hit the target in 5 s?

By what percentage does the resistance of a copper wire ( $\alpha$ = 3.9 $\times$ 10^-3/K)increase when its temperature increases from 20 to 75ºC?

Use the diagram below for the next problem: -Two copper wires have the same volume,but wire 2 is 20% longer than wire 1.The ratio of the resistances of the two wires R₂/R₁ is

If 4.0 $\times$ 10¹⁸ electrons and 1.5 $\times$ 10¹⁸ protons move in opposite directions past a given cross section of a hydrogen discharge tube every second,the average current in the tube is

A 6-V storage battery supplies energy to a simple circuit at the constant rate of 48 W.The resistance of the circuit is

A 20- $\mu$ F capacitor is charged to 200 V and is then connected across a 1000- $\Omega$ resistor.The amount of charge on the capacitor after 10 ms is approximately

A wire of length L = 5.0 m and uniform diameter has an electric field of E = 4.0 V/m throughout the wire.The potential difference across the wire is

You want to measure the current through and the voltage difference across a resistor.How should you connect the ammeter and voltmeter to the resistor?

Lea charges a capacitor and then discharges it through a resistor.She notices that,after three time constants,the voltage across the capacitor has decreased to _____ of its value just prior to the initiation of the discharge.

A potential difference of 120 V produces a current of 8.0 A in the heating element of a toaster.What is the resistance of this heating element while the toaster is carrying this current?