Semiconductor Electronics Materials Devices And Simple Circuits

To solve the problem, we need to understand why photodiodes are operated in reverse bias rather than forward bias.

1. Working of Photodiodes:
Photodiodes are semiconductor devices that generate current when exposed to light. They are primarily used in reverse bias mode to efficiently detect changes in light intensity.

2. Behavior in Reverse Bias:
- In reverse bias, the current through the photodiode is mainly due to minority carriers.
- When light falls on the photodiode, it generates electron-hole pairs. These additional minority carriers significantly increase the reverse current.
- Even a small fractional change in the number of minority carriers results in a measurable change in reverse current, making the photodiode highly sensitive to light.

3. Incorrect Modes:
- Forward bias does not offer significant sensitivity because the current is dominated by majority carriers, and the change due to light is negligible in comparison.

Final Answer:
Photodiodes are mostly operated in reverse biased condition because fractional change in minority carriers produce higher reverse current.

The distance between transmitting and receiving antennas is related to the height of the antennas based on the properties of wave propagation. In general, for electromagnetic waves, the relationship between the height of the antenna and the distance it can effectively transmit is governed by the formula: Let the original height of both antennas be , and the original maximum distance between the antennas be . Now, if the height of both transmitting and receiving antennas is doubled, the new height becomes . Using the proportionality: Since the original distance is proportional to , the new distance will be: Thus, the new distance between the antennas is .

The logic circuit shown involves a combination of NAND gates. Let's break down the behavior of the circuit based on the inputs:

1. The first gate is a NAND gate. A NAND gate outputs 1 unless both its inputs are 1.

For inputs A = 1, B = 0 at this gate, the output will be 1 (since , and the NAND of 0 is 1).

2. The second gate is another NAND gate. The input to this gate comes from the output of the first gate and the input C.

Now, the input to the second gate will be and .

Since the NAND of , the output of the second gate will be 0.

Thus, the correct inputs that produce the output 1 are:

A = 1, B = 0, C = 1

Hence, the correct choice is Option (3).