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Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question (b) - 2014
Question (b)
Read the following passage and answer the accompanying questions. Silicon At the end of June 1948, Bell Labs announced the invention of the transistor by Shockley,... show full transcript
Worked Solution & Example Answer:Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question (b) - 2014
Step 1
Draw a labelled diagram to show the basic structure of a transistor.
Answer
A labelled diagram of a transistor should include:
- n-p-n or p-n-p layers: Clearly label the three layers of the transistor.
- Collector: This is the terminal that collects charge carriers.
- Base: This layer controls the transistor's operation.
- Emitter: The emitter provides charge carriers to the base.
Make sure to show these components correctly in the diagram.
Step 2
State the relationship between the three currents flowing in a transistor.
Answer
The relationship between the three currents in a transistor is given by the equation:
Where:
- is the emitter current,
- is the base current,
- is the collector current.
This indicates that the total emitter current is the sum of the base current and collector current.
Step 3
Draw a circuit diagram for a voltage amplifier.
Answer
The voltage amplifier circuit diagram should depict:
- A transistor connected in series with a resistor.
- Include an input voltage source connected to the base of the transistor.
- The output voltage should be taken across the collector resistor.
Ensure that the connections are clearly labeled.
Step 4
Draw the symbol and truth table for an AND gate.
Answer
The symbol for an AND gate should be:
- A standard representation showing two inputs and one output.
The truth table for an AND gate is:
| A | B | Output |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
This table shows that the output is only high (1) when both inputs A and B are high (1).
Step 5
Give two ways in which the operation of a photodiode differs from that of an LED.
Answer
- Biasing: A photodiode requires reverse bias to allow current to flow, while an LED operates with forward bias to emit light.
- Light emission: An LED produces light when current flows through it, whereas a photodiode detects light and generates current when exposed to light, not emitting it.
Step 6
Step 7
Explain, with the aid of a labelled diagram, how a ray of light is guided along an optical fibre.
Answer
A ray of light is guided along an optical fibre by:
- Total Internal Reflection: When the angle of incidence of light is greater than the critical angle, light reflects back into the fibre instead of refracting out.
- A labelled diagram should depict light entering the fibre at an angle greater than the critical angle, illustrating this phenomenon.
Step 8
Give an expression for the critical angle of the glass in an optical fibre in terms of the speed of light in the glass and the speed of light in air.
Answer
The expression for the critical angle () is given by: where:
- is the speed of light in the glass,
- is the speed of light in air.
This expresses the relationship between the critical angle and the speeds of light in different media.