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In this lesson, we will learn how to express electric current in terms of the rate of net movement of electric charge past a point in a conducting circuit.

Q1:

How many electrons flow through a point in a wire in 3.00 s if there is a constant current of 4.00 A?

Q2:

A cathode-ray tube (CRT) is a device that produces a focused beam of electrons in a vacuum. The electrons strike a phosphor-coated glass screen at the end of the tube, which produces a bright spot of light. The position of the bright spot of light on the screen can be adjusted by deflecting the electrons with electrical fields, magnetic fields, or both. Although the CRT tube was once commonly found in televisions, computer displays, and oscilloscopes, newer appliances use a liquid crystal display (LCD) or plasma screen. Consider a CRT with an electron beam average current of 31.00 μA. How many electrons strike the screen every 5.0 minutes?

Q3:

The quantity of charge through a conductor is modeled as 𝑄 = 4 . 0 0 𝐶 𝑠 𝑡 − 1 . 0 0 𝐶 𝑠 𝑡 + 6 . 0 0 mC. What is the current at time 𝑡 = 3 . 0 0 s?

Q4:

The current through a conductor is modeled as 𝐼 ( 𝑡 ) = 𝐼 ( 1 6 0 𝜋 𝑡 ) 𝑚 s i n , where 𝑡 is measured in seconds and 𝐼 = 2 . 0 𝑚 A. Find the number of electrons flowing through the conductor from 𝑡 = 0 . 0 s to 𝑡 = 5 . 0 s .

Q5:

The charge that flows through a point in a wire as a function of time is modeled as 𝑞 ( 𝑡 ) = 𝑞 𝑒 𝑜 − 𝑡 𝑇 , where 𝑞 = 5 . 0 0 C and 𝑇 = 5 . 0 s.

What is the initial current 𝐼 0 through the wire at time 𝑡 = 0 . 0 0 s?

Find the magnitude of the current at the instant 𝑡 = 0 . 2 5 T.

At what value of 𝑡 will the current be reduced to exactly 2 3 𝐼 0 ?

Q6:

A conductor carries a time-dependent current that decreases exponentially. The instantaneous current is modeled as 𝐼 = 𝐼 𝑒 𝑜 − 𝑡 𝜏 , where 𝑡 corresponds to the time the current has persisted for, 𝐼 = 1 . 5 0 𝑜 A is the current at 𝑡 = 0 . 0 0 s , and the time constant 𝜏 = 0 . 4 0 s . How much charge flows through the conductor between 𝑡 = 0 . 0 0 s and 𝑡 = 2 𝜏 ?

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