Physics 1 Marks Question

Solar cell.

3. Holes are minority carriers and pentavalent atoms are the dopants.

In an n-type silicon, the electrons are the majority carriers, while the holes are the minority carriers. An n-type semiconductor is obtained when pentavalent atoms, such as phosphorus, are doped in silicon atoms.

3. The emitter junction is forward biased and collector junction is reverse biased.

For a transistor action, the junction must be lightly doped so that the base region is very thin. Also, the emitter junction must be forward-biased and collector junction should be reversebiased.

3. Is low at high and low frequencies and constant at mid frequencies.

The voltage gain of a transistor amplifier is constant at mid frequency range only. It is low at high and low frequencies.

3. Hole concentration in p-region is more as compared to n-region.

The diffusion of charge carriers across a junction takes place from the region of higher concentration to the region of lower concentration. In this case, the p-region has greater concentration of holes than the n-region. Hence, in an unbiased p-n junction, holes diffuse from the p-region to the n-region.

3. Lowers the potential barrier.

When a forward bias is applied to a p-n junction, it lowers the value of potential barrier. In the case of a forward bias, the potential barrier opposes the applied voltage. Hence, the potential barrier across the junction gets reduced.

4. Holes are majority carriers and trivalent atoms are the dopants.

In a p-type semiconductor, the holes are the majority carriers, while the electrons are the minority carriers. A p-type semiconductor is obtained when trivalent atoms, such as aluminium, are doped in silicon atoms.

1. (Slightly) decreases.
2. (Slightly) Increases.

Bandgap (1 eV to 1.8 eV)/high absorption coefficient/conductivity 1.

Solar cell.

Collector current decreases slightly.
Base current increases slightly.

A = 0B = 0

LEDs must have band gap in the order of 1.8eV to 3eV but Si & Ge have band gap less than 1.8eV so these cannot be used to fabricate LEDs.

The conductivity of a semiconductor increases with increase of temperature.

Zener diode is used as a voltage regulator.

The sample contains atoms of either original material or the impurity which are all neutral.

Majority charge carriers: electrons and holes.

At absolute zero, a semiconductor has no free charge carrier; hence the electrical conductivity of a semiconductor at absolute zero is zero.

The given diode is reverse biased.

OR, AND and NOT gates.

Holes are charge carriers in p-n-p transistor.

1. Zero
2. Zero.

The repeated use of NAND or NOR gates alone can give all basic gates.

Minority charge carriers: electrons and holes.

Germanium, silicon.

As concentration of electrons is more than the concentration of holes, the given extrinsic semiconductor is n-type.

Holes.

No, the emitter and collector regions cannot be interchanged. Since these are differently doped.

The box contains the circuit of full wave rectifier.

Logic gate ‘1’ is OR gate and logic gate 2 is NOT gate. The combination of gates is NOR gate.

For half wave rectifier, the output frequency = 50Hz.
For full wave rectifier, the output frequency is 100Hz.

b. 10 MHz For beyond the horizon communication, it is necessary for the signal waves to travel a large distance. 10 KHz signals cannot be radiated effeciently because of the antenna size. The high energy signal waves (1GHz - 1000 GHz) penetrate the ionosphere. 10MHz frequencies get reflected easily from the ionosphere. Hence, signal waves of such frequencies are suitable for beyond the horizon communication. Therefore the answer is (b)

The energy gap decreases.

The energy gap in a semiconductor is of the order of 1 eV.

Ratio = 1 : 1.