1. Electromagnetic induction mainly refers to the production of ______ in a circuit because the magnetic flux linked with it changes.
ⓐ. magnetic flux with no change
ⓑ. ordinary resistance of the wire
ⓒ. steady current from unchanged flux
ⓓ. induced emf
Correct Answer: induced emf
Explanation: Electromagnetic induction means that an emf is produced when the magnetic flux linked with a circuit changes. The word induced shows that this emf is not supplied directly by a battery in that situation. A changing magnetic environment, such as a moving magnet near a coil, can create this effect. The induced emf may drive a current if the conducting path is complete. The central idea is flux change, not the mere presence of a magnetic field.
2. A bar magnet is held fixed near a closed coil connected to a sensitive galvanometer. What is expected after the magnet and coil have both become stationary?
ⓐ. The coil shows induced current at rest
ⓑ. The galvanometer shows no deflection
ⓒ. A steady deflection remains in the galvanometer
ⓓ. A momentary deflection continues without flux change
Correct Answer: The galvanometer shows no deflection
Explanation: A stationary magnet near a stationary coil may provide magnetic flux, but the flux linked with the coil is not changing. Electromagnetic induction needs a change in magnetic flux, not just the existence of flux. When the magnet is moved toward or away from the coil, the linked flux changes and a momentary induced current can appear. After both are at rest, there is no continuing cause for induced emf. A closed path is not enough by itself; the magnetic condition must also vary.
3. An open conducting loop is moved near a magnet so that the magnetic flux linked with the loop changes. The most suitable conclusion is that
ⓐ. induced current must flow, but induced emf is impossible
ⓑ. neither induced emf nor flux change is possible in an open loop
ⓒ. induced emf may exist without induced current
ⓓ. induced current flows without any need for charge motion
Correct Answer: induced emf may exist without induced current
Explanation: A changing magnetic flux can produce induced emf even if the circuit is open. Current, however, needs a complete conducting path so that charges can circulate. In an open loop, the induced emf may appear across the gap, but continuous current cannot pass through the broken path. This is similar to a cell having emf even when no external circuit is connected. The condition for emf is flux change, while the condition for current is a closed circuit.
4. In a simple magnet-coil observation, the galvanometer deflects when the magnet is pushed toward the coil and deflects oppositely when the magnet is pulled away. What does the reversal mainly show?
ⓐ. The galvanometer measures only resistance
ⓑ. The induced direction is fixed for every motion
ⓒ. The direction depends on the flux change
ⓓ. The coil changes its material during motion
Correct Answer: The direction depends on the flux change
Explanation: Pushing the magnet toward the coil and pulling it away change the linked magnetic flux in opposite ways. Because the nature of the flux change reverses, the induced emf and current direction also reverse. The galvanometer deflection is a visible sign of the current direction in the circuit. The coil material and the permanent magnet are not required to change for this observation. Direction in induction is connected with the change being produced, not merely with the name of the magnet pole.
5. A hand-driven generator produces electrical output when its coil is rotated in a magnetic field. This device is based mainly on
ⓐ. direct conversion of resistance into emf
ⓑ. electromagnetic induction
ⓒ. heating of a resistor by steady current
ⓓ. production of emf by steady flux alone
Correct Answer: electromagnetic induction
Explanation: A generator works by rotating a coil in a magnetic field so that the magnetic flux linked with the coil changes continuously. This changing flux produces an induced emf. The mechanical work used to rotate the coil is converted into electrical energy through electromagnetic induction. Heating may occur in practical circuits, but it is not the basic operating principle of the generator. The essential action is changing flux through the coil, not rubbing charges or changing resistance.
6. A coil connected to a galvanometer is placed near another coil carrying current. A momentary galvanometer deflection is observed when the current in the nearby coil is switched on. The deflection occurs because
ⓐ. the nearby coil produces a steady field only
ⓑ. a sudden flux change links the second coil
ⓒ. the galvanometer coil changes its own resistance
ⓓ. the secondary flux remains constant during switching
Correct Answer: a sudden flux change links the second coil
Explanation: When current in the nearby coil changes from zero to a finite value, the magnetic field produced by it changes. This changing field changes the magnetic flux linked with the second coil. The changing flux produces an induced emf, and the closed galvanometer circuit allows a momentary current. Once the nearby current becomes steady, the linked flux stops changing and the deflection does not continue. The induction is caused by magnetic coupling, not by physical contact between the coils.
7. For discussing electromagnetic induction in a coil, the most directly relevant prerequisite set is
ⓐ. magnetic field, area, conducting path
ⓑ. current, focal length, and coil area
ⓒ. magnetic flux, density, and liquid depth
ⓓ. magnetic field, resistance, and open gap
Correct Answer: magnetic field, area, conducting path
Explanation: Induction is connected with magnetic flux, and flux depends on magnetic field and the surface area linked with the circuit. A conducting path is also needed if the induced emf is to drive an induced current. The shape and orientation of the coil matter because they affect how much magnetic field passes through the surface. The other sets belong to different areas of physics and do not describe magnetic flux change. The starting quantities are magnetic and circuit quantities, not optical or fluid variables.
8. The phrase induced emf is best understood as
ⓐ. emf due to changing magnetic flux
ⓑ. force on charges without flux change
ⓒ. the current produced by a chemical source
ⓓ. resistance produced by a changing field
Correct Answer: emf due to changing magnetic flux
Explanation: Induced emf is the emf that appears because the magnetic flux linked with a circuit changes. It is not necessarily supplied by a chemical cell. If the circuit is closed, this emf can drive an induced current through the circuit resistance. If the circuit is open, the emf may still be present even though continuous current cannot flow. The word emf refers to energy supplied per unit charge, while current refers to the rate of flow of charge.
9. One setup has a coil and magnet at rest relative to each other. Another setup has the same magnet moving toward the same coil. The second setup is more likely to show induction because
ⓐ. motion makes the magnet field steady everywhere
ⓑ. relative motion changes linked flux
ⓒ. relative motion keeps the linked flux constant
ⓓ. the wire charges stop responding to fields
Correct Answer: relative motion changes linked flux
Explanation: Relative motion between a magnet and a coil can change the magnetic flux linked with the coil. When the magnet approaches, the magnetic field through the coil usually changes with time. This time variation of flux is what produces induced emf. In the stationary case, the linked flux may be non-zero but unchanged, so no continuing induced emf is produced. The motion matters because it changes the magnetic condition experienced by the circuit.
10. Two observations are made with the same coil and magnet:
I. The magnet is moved slowly toward the coil.
II. The magnet is moved faster toward the coil through the same path.
The better comparison is
ⓐ. both observations must give zero induced emf because the same magnet is used
ⓑ. observation II gives smaller induced emf because magnetic flux cannot change quickly
ⓒ. observation II gives larger induced emf because the flux changes more rapidly
ⓓ. observation I gives larger induced emf because the motion is slower
Correct Answer: observation II gives larger induced emf because the flux changes more rapidly
Explanation: The magnitude of induced emf depends on how rapidly the magnetic flux changes. Moving the same magnet faster through the same path produces a greater rate of flux change. The coil and magnet being the same does not make the induced emf the same, because time taken for the change also matters. A slow motion gives a smaller rate of change and hence a smaller deflection. The comparison is based on rate of flux change, not only on the final and initial positions.
11. The symbol \(\vec{B}\) in electromagnetic induction represents
ⓐ. magnetic field
ⓑ. angular displacement of a coil
ⓒ. resistance of the circuit
ⓓ. electric charge
Correct Answer: magnetic field
Explanation: The symbol \(\vec{B}\) represents magnetic field, often called magnetic flux density in this context. It is a vector quantity, so its direction matters while deciding flux and induction effects. Magnetic flux depends on how \(\vec{B}\) is oriented relative to the surface linked with the circuit. Resistance is usually represented by \(R\), current by \(I\), and emf by \(\varepsilon\). Confusing \(\vec{B}\) with \(R\) would mix a field quantity with a circuit property.
12. Use the arrangement described below. A flat circular loop lies on a table, and the area vector \(\vec{A}\) is assigned to the loop. The direction of \(\vec{A}\) is
ⓐ. along the wire of the loop
ⓑ. always along the current in the loop
ⓒ. always opposite to the magnetic field \(\vec{B}\)
ⓓ. normal to the plane of the loop
Correct Answer: normal to the plane of the loop
Explanation: The area vector \(\vec{A}\) of a plane surface is drawn perpendicular to the surface. For a flat loop on a table, \(\vec{A}\) points normal to the plane of the table, depending on the chosen side of the surface. It is not drawn along the wire because the wire is only the boundary of the surface. It also does not automatically follow the current or oppose the magnetic field. The angle used in flux is the angle between \(\vec{B}\) and \(\vec{A}\), so the normal direction is essential.
13. A unit record for the basic quantities in induction contains one mismatched entry. Identify the mismatched entry.
| Row | Quantity | Usual SI unit |
|---|
| P | Magnetic field \(\vec{B}\) | \(T\) |
| Q | Area \(A\) | \(m^2\) |
| R | Emf \(\varepsilon\) | \(V\) |
| S | Resistance \(R\) | \(A\) |
ⓐ. Row Q
ⓑ. Row R
ⓒ. Row P
ⓓ. Row S
Correct Answer: Row S
Explanation: Magnetic field \(\vec{B}\) is measured in tesla, written as \(T\). Area \(A\) is measured in square metre, written as \(m^2\). Emf \(\varepsilon\) is measured in volt, written as \(V\). Resistance \(R\) is not measured in ampere; ampere is the unit of current \(I\). Resistance is measured in ohm, written as \(\Omega\), so the mismatch is in the resistance row.
14. Fleming's right-hand rule is used in a generator-type situation mainly to find the direction of
ⓐ. induced current
ⓑ. area vector of a coil
ⓒ. direction of motor force
ⓓ. resistance change in a wire
Correct Answer: induced current
Explanation: Fleming's right-hand rule is used when a conductor moves in a magnetic field and an induced current is produced. In this rule, the thumb represents motion, the forefinger represents magnetic field, and the middle finger represents induced current. It is associated with generator action, where mechanical motion produces electrical output. It should not be confused with Fleming's left-hand rule, which is used for motor force on a current-carrying conductor. The right-hand rule connects motion, field, and induced current direction.
15. Match the basic symbols with their usual meanings.
| Column I | Column II |
|---|
| P. \(I\) | 1. Resistance |
| Q. \(R\) | 2. Current |
| R. \(\varepsilon\) | 3. Magnetic flux |
| S. \(\phi_B\) | 4. Emf |
ⓐ. P-1, Q-2, R-4, S-3
ⓑ. P-2, Q-4, R-1, S-3
ⓒ. P-2, Q-1, R-4, S-3
ⓓ. P-3, Q-1, R-4, S-2
Correct Answer: P-2, Q-1, R-4, S-3
Explanation: The symbol \(I\) represents electric current, and its SI unit is ampere \(A\). The symbol \(R\) represents resistance, measured in ohm \(\Omega\). The symbol \(\varepsilon\) is commonly used for emf, measured in volt \(V\). Magnetic flux is represented by \(\phi_B\), where the subscript reminds us that the flux is due to magnetic field. Keeping \(I\), \(R\), \(\varepsilon\), and \(\phi_B\) separate prevents mixing circuit response with magnetic flux change.
16. The angle \(\theta\) used while discussing magnetic flux through a plane surface is normally taken between
ⓐ. \(\vec{B}\) and the area vector \(\vec{A}\)
ⓑ. current \(I\) and resistance \(R\)
ⓒ. emf \(\varepsilon\) and current \(I\)
ⓓ. \(\vec{B}\) and the plane of the surface
Correct Answer: \(\vec{B}\) and the area vector \(\vec{A}\)
Explanation: In magnetic flux, the surface is represented by its area vector \(\vec{A}\), not merely by the flat plane itself. The area vector is perpendicular to the surface. The standard angle \(\theta\) is measured between \(\vec{B}\) and \(\vec{A}\). If the angle is mistakenly measured with the plane of the surface, the orientation condition becomes reversed. This convention becomes essential when using the relation \(\phi_B=BA\cos\theta\) later.
17. A conducting loop has resistance \(R\) and is placed in a changing magnetic environment. The role of \(R\) is most directly connected with
ⓐ. making the area vector parallel to the wire
ⓑ. creating magnetic flux even when no field is present
ⓒ. current response to a given induced emf
ⓓ. replacing the need for a closed conducting path
Correct Answer: current response to a given induced emf
Explanation: Resistance \(R\) is a circuit property that controls current for a given emf. In induction, the changing magnetic flux is responsible for producing the induced emf. If the circuit is closed, the induced emf can drive current through the resistance. A larger resistance gives a smaller current for the same emf. Resistance does not create magnetic flux by itself and does not decide the direction of the area vector.
18. Read the short case below.
Case 1: A magnet moves near a closed conducting ring. Case 2: The same magnet moves in the same way near a ring with a small break in it.
What comparison is most suitable?
ⓐ. Only Case 2 can have induced current because the ring is open
ⓑ. Neither case can have induced emf because motion is involved
ⓒ. Case 1 has no flux change because the path is closed
ⓓ. emf in both cases, current only in Case 1
Correct Answer: emf in both cases, current only in Case 1
Explanation: In both cases, the moving magnet can change the magnetic flux linked with the ring. A changing flux can produce induced emf even when the ring has a break. Continuous induced current needs a closed conducting path, which is available only in Case 1. In Case 2, charges may separate and an emf may appear across the gap, but charge cannot circulate around the full ring. The comparison separates the cause of induced emf from the circuit condition needed for current.
19. Magnetic flux through a surface gives a measure of
ⓐ. the charge stored on the boundary of the surface
ⓑ. magnetic field through the chosen surface
ⓒ. the heat produced per second in the surface
ⓓ. the resistance offered by the surface to current
Correct Answer: magnetic field through the chosen surface
Explanation: Magnetic flux is used to describe how much magnetic field is linked with a given surface. It depends on the magnetic field strength, the area of the surface, and the orientation of the surface with respect to the field. A large surface in a strong magnetic field can have large flux only when the field actually passes through it effectively. The boundary wire alone is not enough to decide flux; the surface enclosed by it is important. Flux is therefore a field-through-area idea, not a resistance or heating quantity.
20. A plane loop is placed in a uniform magnetic field. The magnetic flux linked with it changes when
ⓐ. the loop is observed from a different side without physical change
ⓑ. only the material of the supporting stand is changed
ⓒ. the name of the loop shape is changed without changing its area
ⓓ. the loop is rotated so that its surface orientation changes
Correct Answer: the loop is rotated so that its surface orientation changes
Explanation: Magnetic flux depends on the orientation of the surface relative to the magnetic field. Rotating the loop changes the angle between \(\vec{B}\) and the area vector \(\vec{A}\), so the effective field passing through the loop can change. Merely changing the stand or the observer's viewpoint does not physically change the linked flux. The area and magnetic field may remain the same, yet the flux can still change due to orientation. This is why rotating coils are useful in induction devices.
