Electromagnetic brakes work on the principle of electromagnetic induction. If a metallic disc or a coil is rotating in a uniform magnetic field, it will experience a torque due to induced currents set up in the disc. According to Lenz's law, induced current is in a direction so as to oppose the rotation. Hence a retarding torque is produced. The rotating wheel of a vehicle is connected to a coil placed in a uniform emf is used to charge a battery. Thus kinetic enery of wheel is stored as chemical energy. The drawback of electromagnetic brake is that induced current or retarding torque is directly proportional to speed of rotation. The speed, therefore, decays exponentially and vehicle will take a long time to stop. Thus, mechanical brakes are used simultaneously.
The main disadvantage of electromagnetic brakes is that

Options

A. It cannot bring the vehicle to a halt
B. It has a complicated procedure
C. It wastes energy due to induced emf
D. It cannot provide a large braking force

Answer

To solve the question regarding the main disadvantage of electromagnetic brakes, we can break it down into a step-by-step analysis:

### Step 1: Understand the Principle of Electromagnetic Brakes
Electromagnetic brakes operate based on electromagnetic induction. When a metallic disc or coil rotates in a magnetic field, it experiences a torque due to the induced currents.

**Hint:** Recall the principle of electromagnetic induction and how it relates to the motion of conductors in magnetic fields.

### Step 2: Analyze the Effect of Induced Current
According to Lenz's law, the direction of the induced current is such that it opposes the cause of its induction, which in this case is the rotation of the disc. This results in a retarding torque that slows down the rotation.

**Hint:** Remember Lenz's law and how it applies to induced currents in rotating systems.

### Step 3: Consider the Relationship Between Speed and Retarding Torque
The retarding torque produced by the induced current is directly proportional to the speed of rotation. As the speed decreases, the induced current and thus the retarding torque also decrease.

**Hint:** Think about how the relationship between speed and torque affects the braking process.

### Step 4: Evaluate the Stopping Time
Since the retarding torque decreases with speed, the vehicle takes a longer time to come to a complete stop. This exponential decay in speed means that the vehicle cannot be halted quickly.

**Hint:** Consider the implications of exponential decay in speed on the effectiveness of the braking system.

### Step 5: Identify the Main Disadvantage
From the analysis, it is clear that the main disadvantage of electromagnetic brakes is that they cannot bring the vehicle to a halt quickly. This necessitates the use of mechanical brakes to assist in stopping the vehicle effectively.

**Hint:** Focus on the key point that distinguishes electromagnetic brakes from mechanical brakes in terms of stopping capability.

### Conclusion
The main disadvantage of electromagnetic brakes is that they cannot bring the vehicle to a halt quickly, leading to the need for additional mechanical braking systems.

### Final Answer
The main disadvantage of electromagnetic brakes is that they cannot bring the vehicle to a halt quickly.