Transformers

Step 1: Concept
For an ideal transformer, the ratio of currents is inversely proportional to the turns ratio: .
Step 2: Analysis
Given and .
.
Step 3: Conclusion
The primary current .
Final Answer: (A)

Step 1: Process
Froth floatation is used primarily to concentrate sulphide ores based on the differential wetting properties of the ore and gangue.
Step 2: Analysis
- Zincite ( ) is an oxide ore.
- Bauxite ( ) is an oxide ore.
- Malachite [ ] is a carbonate ore.
Step 3: Identification
Cinnabar ( ) is a sulphide ore.
Step 4: Conclusion
Therefore, cinnabar is concentrated using the froth floatation process.
Final Answer: (b)

Step 1: Formula
The transformer ratio is .
Step 2: Values
.
Step 3: Calculation
.
Final Answer: (a)

Step 1: Recall the transformer equation.
The voltage ratio in a transformer is related to the turn ratio as: where and are the voltages across the primary and secondary coils, respectively, and and are the number of turns in the primary and secondary coils.

Step 2: Analyze the given information.
For a step-up transformer with a turn ratio of 1:2, the voltage across the secondary should ideally be twice the primary voltage. However, a Leclanché cell has a very low emf of 1.5 V, and transformers do not work efficiently with DC sources, so the secondary voltage is essentially zero.

Step 3: Conclusion.
The voltage across the secondary is zero, which is option (3).

Step 1: Understanding the Concept:
Magnifying power of telescope = ratio of angle subtended at eye by image to angle subtended by object. For distant objects, it also equals .
Step 2: Detailed Explanation:
A telescope makes objects appear closer, not larger. Magnifying power 10 means object appears 10 times nearer. The angular size increases, but the perceived effect is that the object is brought 10 times closer.
Step 3: Final Answer:
Thus, tree appears 10 times nearer.

Concept: Transformer works only with alternating current (AC), not direct current (DC).

Step 1: Given input.
A cell provides DC.

Step 2: Working principle.
Transformer requires changing magnetic flux.

Step 3: Conclusion.
No changing flux no induced emf.