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Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2015
Question 11
Read the following passage and answer the accompanying questions. In the years since his death, Nikola Tesla (1856–1943) has enjoyed a curious legacy. On the one ha... show full transcript
Worked Solution & Example Answer:Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2015
Step 1
Define the tesla.
Answer
The tesla (T) is the unit of measurement for magnetic flux density in the International System of Units (SI). It is defined as the amount of magnetic flux density, such that 1 tesla is equivalent to 1 weber per square meter. This unit quantifies the strength of a magnetic field.
Step 2
Sketch voltage-time graphs for (i) an a.c. supply.
Answer
For an a.c. supply, the voltage-time graph is a sinusoidal wave. The y-axis represents voltage, while the x-axis represents time. The wave oscillates above and below the zero voltage level, indicating the alternating nature of the current.
+
| . . .
| . . . . . .
| . .
---+-------------------------
| . .
| . .
-+ . . .
(ii) For a d.c. supply, the voltage-time graph remains constant over time.
+
|***********
|***********
|***********
---+-------------------------
|_________________________
-
Step 3
Explain the term electromagnetic induction.
Answer
Electromagnetic induction refers to the production of an electromotive force (emf) across a conductor when it is exposed to a varying magnetic field. This phenomenon is governed by Faraday's Law, which states that the induced emf in a circuit is directly proportional to the rate of change of the magnetic flux through the circuit.
In simple terms, when the magnetic field around a conductor changes, it induces a voltage, allowing for the generation of electric current.
Step 4
Why does a transformer not work with direct current?
Answer
A transformer operates on the principle of electromagnetic induction, which requires a changing magnetic field to induce voltage in the secondary coil. Direct current (DC) does not produce a changing magnetic field; it maintains a constant current. Therefore, when a transformer is supplied with DC, it cannot induce a voltage across its secondary coil, rendering it ineffective.
Step 5
Why is it inefficient to use low voltage when transmitting electricity?
Answer
Transmitting electricity at low voltage is inefficient due to the following reasons:
- Large Current: A lower voltage requires a higher current to deliver the same power (P = VI). Higher currents increase heating in the wires due to resistance (I²R losses).
- More Heat Lost: The increased heating leads to energy loss in the form of heat, making the transmission less efficient overall.
Step 6
Step 7
Explain why it is necessary to use the rms voltage when comparing a.c. and d.c. electricity.
Answer
Using the rms voltage is essential because it allows for accurate power comparisons between alternating current (a.c.) and direct current (d.c.). The rms value of a.c. gives the equivalent d.c. voltage that would deliver the same power to a load. This means that when analyzing electrical systems, the rms voltage provides a consistent basis for comparing the two types of current.
Step 8
Give one advantage and one disadvantage of electric cars.
Answer
Advantage: Electric cars typically have fewer carbon emissions compared to conventional vehicles, leading to a smaller environmental footprint and cleaner air.
Disadvantage: A significant drawback of electric cars is their shorter range compared to gasoline vehicles, often leading to concerns about battery life and charging infrastructure.