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Chapter 21: Q19CQ (page 772)

Can all of the currents going into the junction in figure below be positive? Explain.

Short Answer

Expert verified

At least one of the currents flowing through a junction should be negative.

Step by step solution

01

Kirchhoff's first law

Kirchhoff's first law states that, in a circuit, the sum of currents flowing towards a particular junction should be equal to the sum of currents flowing away from that junction.

02

Step 2:

According to Kirchhoff's first law, the sum of currents flowing through a junction has to be zero. If we have three currents\({I_1}\),\({I_2}\)and\({I_3}\), then-

\[\begin{array}{l}{I_1} + {I_2} + {I_3} = 0\\{I_1} + {I_2} = - {I_3}\end{array}\]

From the above relation, it is clear that at least one of the currents should be negative, then only the sum of currents will be zero.

Thus, all the currents flowing through the junction cannot be positive.

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Most popular questions from this chapter

Standard automobile batteries have six lead-acid cells in series, creating a total emf of 12.0 V. What is the emf of an individual lead-acid cell?

Carbon-zinc dry cells (sometimes referred to as non-alkaline cells) have an emf of 1.54 V, and they are produced as single cells or in various combinations to form other voltages. (a) How many 1.54 V cells are needed to make the common 9 V battery used in many small electronic devices? (b) What is the actual emf of the approximately 9 V battery? (c) Discuss how internal resistance in the series connection of cells will affect the terminal voltage of this approximately 9 V battery.

Verify the second equation in Example 21.5 by substituting the values found for the currents l1andl2

Why is the power dissipated by a closed switch, such as in Figure 21.43, small?

(a) What is the terminal voltage of a large 1.54 v carbon-zinc dry cell used in a physics lab to supply 2.00 a to a circuit, if the cell's internal resistance is 0.100Ω ? (b) How much electrical power does the cell produce? (c) What power goes to its load?
See all solutions

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