Physics: Principles and Problems
Physics: Principles and Problems
9th Edition
Elliott, Haase, Harper, Herzog, Margaret Zorn, Nelson, Schuler, Zitzewitz
ISBN: 9780078458132
Textbook solutions

All Solutions

Page 789: Section Review

Exercise 27
Step 1
1 of 3
In this problem, we are given a transistor circuit in which the current gain from base to collector is 95. We are asked to find the ration between the emitter current and the base current.
Step 2
2 of 3
In order to do this, we are going to start from the equation of the transistor
$I_E=I_B+I_C$
and since we know that $I_C/I_B=95$ so we can write

$$
frac{I_E}{I_B}=1+frac{I_C}{I_B}=1+95=boxed{96}
$$

Result
3 of 3
$$
frac{I_E}{I_B}=96
$$
Exercise 28
Step 1
1 of 4
In this problem, we are given a forward-biased diode with a constant voltage drop of about 0.7 V for which the battery voltage is increased by 1 V. We are asked to find the increase of the voltage across the diode and across the resistor increase and by how much does the current increase through the resistor.
Step 2
2 of 4
a) Since the voltage across the diode is constantly 0.7 V the entirety of the voltage increase will occur across the resistor, i.e. $boxed{textrm{1 V}}$.
Step 3
3 of 4
b) Now, we can find that the current increase is given from the Ohm’s law as follows

$$
Delta I=frac{Delta V}{R}=boxed{frac{1textrm{ V}}{R}}
$$

Result
4 of 4
a) The voltage across the diode is unchanged and across the resistor increases by 1 V

b) The increase in the current is $Delta I =frac{1 textrm{ V}}{R}$.

Exercise 29
Step 1
1 of 1
The $pn$-junction diodes by definition conduct currents much better when forward-biased i.e. they have much lower resistance in comparison when they are reverse-biased.
Exercise 30
Step 1
1 of 1
In order for LED to emit the light the p-end has to be connected to the positive terminal because it has to be forward-biased.
Exercise 31
Step 1
1 of 3
In this problem we are given the base and the collector currents in a transistor and we are asked to find the current gain in this transistor.
Step 2
2 of 3
We can do so by using the definition of the current gain which is given as

$$
G=frac{I_C}{I_B}=frac{6.6times 10^{-3}}{0.055times 10^{-3}}=boxed{120}
$$

Result
3 of 3
$$
G=120
$$
Exercise 32
Step 1
1 of 1
Although in principle, one can think of this as possible, in reality, due to the different characteristics of the electronic elements this is impossible. The reason for this is the fact that in diode the $p$-end is approximately of the same thickness as the $n$-end. So if we would merge two diodes together, the $p$-layer would be twice as thick as the respective $n$-ends. However, in an $npn$ transistor, $p$-end is thin enough to allow for the passage of electrons so the former construction would not resemble a transistor whatsoever.
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