Eddy currents testing MCQ

Eddy current : Circulating currents induced in a metal block, when it is moving in a magnetic field or placed in a changing magnetic field are called eddy current.

1. It flows in a close loops within the metal plate. These currents are produce in a metal plate when it is placed in changing magnetic field.
2. These are produced in the cores of transformer, in induction coil, electric motor, electromagnet.
3. These currents are not produce in an insulator and semiconductor at low temperature.
4. According to Lenz’s law, the eddy current opposes the cause that produces it.
5. The direction of eddy current is given by Lenz’s law or Flemming’s right hand rule.
6. The damping effect and heating effect of eddy current is used in several applications. Eddy current do not produce sparking as path is circulating.
7. Application of eddy currents: Dead beat galvanometer. (electromagnetic damping), Induction furnace, Electric brakes, Speedometer.

Eddy Current Testing MCQs

1. Eddy currents are_________

(a) induced currents due to changing magnetic flux

(b) induced currents in magnetic field

(c) induced currents in material

(d) uniform currents in conductor

Answer: A

2. Eddy currents have very large magnitude as_________

(a) they are induced currents

(b)  they are circulating currents

(c) the resistance of metals is very small

(d) magnetic field is very strong

Answer: C

3. The plane in which eddy currents are produced in a conductor is inclined to the plane of the magnetic field at an angle of___________

(a) 60°

(b) 90°

(c) 180°

(d) 45°

Answer: B

4. Eddy currents do not cause_______

(a) sparking

(b) damping

(c) heating

(d) loss of energy

Answer: A

5. Which of the following is not the application of eddy currents_______

(a) speedometer

(b) induction furnace

(c) dead beat galvanometer

(d) Xray crystallographer

Answer: D

6. Heat produced in the induction furnace is very large because__________

(a) it uses eddy currents

(b) magnitude of eddy current is very large

(c) eddy currents are produced for long time

(d) both ‘a’ and ‘c’

Answer: B

7. The core used in a transformer and other electromagnetic devices is laminated so that___________

(a) ratio of voltage in the primary and secondary may be increased

(b) energy loss due to eddy currents may be minimized

(c) the weight of the transtormer may be reduced

(d) residual magnetism in the core may be reduced

Answer: B

8. Eddy currents have very large magnitude as_________

(a) they are induced currents

(b) they are circulating currents

(c) the resistance of metals is very small

(d) magnetic field is very strong

Answer: C

9. In a galvanometer the coil is wound on a bad conductor, the eddy current will be________

(a) zero

(b) minimum

(c)maximum

(d) 50% of the actual value

Answer: A

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