Ch. 40 - Molecules and Solids

Giancoli Douglas - Physics for Scientists and Engineers 5th edition

Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Not the one you use?Change textbook

Giancoli Douglas 5th edition

Ch. 40 - Molecules and Solids

Problem 65

Chapter 37, Problem 65

(II) From Fig. 40–49, write an equation for the relationship between the base current (I_B), the collector current (I_c), and the emitter current (I_E), not labeled in Fig. 40–49). Assume the ac current i_B= i_C = 0.

Name: Physics for Scientists and Engineers
Author: Giancoli Douglas
ISBN: 9780137488179

Verified step by step guidance

Identify the components of the transistor circuit: The base current (I_B), collector current (I_C), and emitter current (I_E) are related in a transistor. The emitter current is the sum of the base current and the collector current.

Write the general current relationship for a transistor: Using Kirchhoff's Current Law (KCL), the total current entering or leaving a junction must equal zero. For a transistor, this means I_E = I_B + I_C.

Assume the AC components of the currents are zero: The problem states that i_B = i_C = 0, which means we are only considering the DC components of the currents.

Express the relationship in terms of the DC currents: Since the AC components are zero, the relationship simplifies to I_E = I_B + I_C, where all terms represent the DC currents.

Conclude with the final equation: The relationship between the base current, collector current, and emitter current is I_E = I_B + I_C. This equation is fundamental for understanding current flow in a transistor.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Transistor Operation

Transistors are semiconductor devices that can amplify or switch electronic signals. In a bipolar junction transistor (BJT), the relationship between the base current (I_B), collector current (I_C), and emitter current (I_E) is fundamental. The transistor operates in three regions: active, cutoff, and saturation, with the active region being crucial for amplification, where I_E is the sum of I_B and I_C.

Current Relationships in BJTs

In a BJT, the currents are related by the equation I_E = I_B + I_C. This relationship indicates that the emitter current is the total current flowing out of the emitter terminal, which is the sum of the base current and the collector current. Understanding this relationship is essential for analyzing transistor circuits and their behavior in various configurations.

AC Analysis in Transistors

AC analysis in transistor circuits involves examining how the circuit responds to alternating current signals. In the context of the question, assuming that the AC currents I_B and I_C are zero simplifies the analysis, allowing us to focus on the DC operating point. This assumption helps in deriving the relationship between the currents without the complications introduced by AC variations.

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Textbook Question

If the current gain of the transistor amplifier in Fig. 40–49 is β = i_c/i_B = 95, what value must R_c have if a 1.0-μA ac base current is to produce an ac output voltage of 0.40 V?

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Textbook Question

(III) A 120-V rms 60-Hz voltage is to be rectified with a full-wave rectifier as in Fig. 40–40, where R = 24 kΩ, and C = 35 μF. (a) Make a rough estimate of the average current. (b) What happens if C = 0.10 μF? [Hint: See Section 26–5.]

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Textbook Question

(II) An ac voltage of 120 V rms is to be rectified. Estimate very roughly the average current in the output resistor R (42 kΩ) for (a) a half-wave rectifier (Fig. 40–39), and (b) a full-wave rectifier (Fig. 40–40) without capacitor.

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Textbook Question

A zener diode voltage regulator is shown in Fig. 40–55. Suppose that R = 2.80 kΩ and that the diode breaks down at a reverse voltage of 130 V. (The current increases rapidly at this point, as shown on the far left of Fig. 40–38 at a voltage of -12V on that diagram.) The diode is rated at a maximum current of 120 mA. (a) If R_load = 21.0 kΩ, over what range of supply voltages will the circuit maintain the output voltage at 130 V? (b) If the supply voltage is 275 V, over what range of load resistance will the voltage be regulated?

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Textbook Question

One possible form for the potential energy (U) of a diatomic molecule (Fig. 40–8) is called the Morse Potential:

$U = U_{0} {[1 - e^{- a (r - r_{0})}]}^{2}$

(a) Show that r₀ represents the equilibrium distance and U₀ the dissociation energy.

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(II) From Fig. 40–49, write an equation for the relationship between the base current (IB), the collector current (Ic), and the emitter current (IE), not labeled in Fig. 40–49). Assume the ac current iB = iC = 0.

Key Concepts

Transistor Operation

Current Relationships in BJTs

AC Analysis in Transistors

(II) From Fig. 40–49, write an equation for the relationship between the base current (I_B), the collector current (I_c), and the emitter current (I_E), not labeled in Fig. 40–49). Assume the ac current i_B= i_C = 0.