Electric Field and Electric Field Lines

Correct answer: A. Zero

Explanation: Electric field is defined as force per unit positive test charge: E = F/q. Therefore, for a finite test charge q placed at a point where the resultant electric field is E = 0, the electric force is F = qE = 0. This conclusion concerns the electric force produced by the specified field; other forces, such as gravity, are outside the question. Option A is correct, while the other choices confuse field, charge, and force.

Correct answer: A. Between large oppositely charged parallel plates

Explanation: The region between two large, oppositely charged parallel plates has an approximately uniform electric field, provided the observation is away from the edges. A uniform field has constant magnitude and direction, so its field lines are straight, parallel, and equally spaced. Around a point charge, the lines are radial and curved in the overall pattern; two like charges also produce a nonuniform field. Thus option A is correct, with edge effects neglected in the ideal model.

Correct answer: A. Towards the left

Explanation: The electric force on a charge is given by F = qE. Electric-field direction is defined as the direction of force on a positive test charge. For a negative charge, q is negative, so the force vector is opposite to the electric-field vector. Since the field points to the right, the force on the negative charge points to the left. The force is not zero unless the field or charge is zero. Thus option A is correct.

Correct answer: A. Upward

Explanation: The force on a charge in an electric field is F = qE. For a positive charge, q is greater than zero, so multiplication by q does not reverse the direction of E. The force therefore points in the same direction as the field. Because the field is upward, the force is upward. A downward force would correspond to a negative charge, while a perpendicular or zero force is not implied here. Hence option A is correct.

Correct answer: A. From positive charge to negative charge

Explanation: By convention, the tangent to an electric-field line gives the direction of the electric field, which is the direction a positive test charge would move initially. Field lines originate on positive charges and terminate on negative charges. Consequently, in the region between opposite charges, the arrows point from the positive charge toward the negative charge. Option B reverses the convention, while C and D do not describe the field-line pattern for unlike charges. Thus option A is correct.

Correct answer: A. Force will be larger

Explanation: The electric-force relation is F = qE, so for a fixed test charge q, the magnitude of force is |F| = |q||E|. Thus increasing the electric-field magnitude increases the force magnitude in direct proportion. Because the test charge is positive, its force remains in the field direction; a larger magnitude does not by itself reverse that direction. It also cannot make the force zero. Hence option A is correct.

Correct answer: A. Vector quantity

Explanation: Electric field at a point is defined as force per unit positive test charge, E = F/q. Since force is a vector and division by a scalar charge preserves its directional character, electric field has both magnitude and direction. It is therefore a vector quantity. This direction is essential when fields from several charges are combined; their contributions must be added vectorially rather than by magnitudes alone. Hence option A is correct, while B, C, and D incorrectly omit direction.

Correct answer: A. Towards the right

Explanation: The governing rule is that the electric field produced by a positive point charge is directed radially outward from the charge. A point located to the right of the charge has the outward radial direction pointing rightward. Therefore the field at that point is toward the right, which is option A. The leftward direction would apply to a negative charge at the same location, not to a positive one.

Correct answer: A. Towards the left

Explanation: The electric field due to a negative point charge is directed inward, toward the charge. If the observation point lies on the right side of the charge, the direction from that point toward the charge is leftward. Thus option A is correct. A rightward field would be associated with a positive charge at the same location, while upward and downward directions do not follow from this one-dimensional arrangement.

Correct answer: A. Whether the charge is positive or negative

Explanation: The first step is to identify the sign of the source charge because field-line direction depends on it. Lines emerge outward from a positive charge and terminate inward toward a negative charge. This sign rule determines the direction before any diagram is interpreted. Colour, paper shape, and the artist’s line thickness have no physical role. Therefore option A is the correct choice.

Correct answer: B. 7 newton per coulomb towards north

Explanation: Electric field is a vector, so oppositely directed fields must be subtracted algebraically. Taking north as positive, the resultant is E = +12 - 5 = +7 N/C. The positive sign means that the direction remains north, because the 12 N/C field is larger than the 5 N/C field. Thus option B is correct; adding the magnitudes would incorrectly give 17 N/C.

Correct answer: A. Electric field cannot have two directions at the same point

Explanation: By definition, the tangent drawn to an electric field line at any point gives the direction of the electric field at that point. A well-defined electric field has one unique direction at a given point, except at a point where the field itself is zero and direction is undefined. Consequently, two field lines cannot intersect with different tangents. Option A correctly states this rule.

Correct answer: A. Zero

Explanation: A metal is a conductor containing mobile charge carriers. In electrostatic equilibrium, these charges redistribute themselves until the electric field within the conducting material is zero; otherwise a force would continue to drive them. The absence of free charge in the cavity also means no induced inner-surface charge is required. Thus the field inside the metal is zero, so option A is correct.

Correct answer: B. Only direction of field

Explanation: Electric-field-line arrows indicate the direction of the vector field, while the spacing or density of lines represents its relative magnitude. Reversing only the arrows changes the vector from E to −E, so its direction reverses but its magnitude remains unchanged. The geometry and spacing also remain the same. Therefore option B is correct; neither distance nor field strength is altered by changing arrows alone.

Correct answer: A. Strength will be greater

Explanation: The governing representation is field-line density: the closer the lines are, the stronger the electric field is understood to be. If an unchanged number of lines passes through a smaller area, the number of lines per unit area increases. Therefore the local field strength is greater. A smaller area does not make the field zero, and it does not remove the field direction; it indicates greater concentration.

Correct answer: C. Force remains same

Explanation: The governing relation is F = qE, where q is the charge and E is the external electric field. Since neither q nor E changes, the electric force remains unchanged, so option C is correct. Increasing mass changes the acceleration according to a = F/m, making the acceleration smaller, but it does not alter the electric force itself. Options A and B confuse force with acceleration, while D is incorrect because the charge is still present in a nonzero field.

Correct answer: A. Because field lines go inward for a negative charge

Explanation: Electric-field direction is defined as the direction of force on a small positive test charge. A negative source charge attracts that positive test charge, so the field vector points toward the negative charge. Consequently, electric-field lines terminate on a negative charge and do not emerge from it; option A is correct. Option B is false because a negative charge does produce a field, while C and D do not describe the relevant rule.

Correct answer: A. Field lines start from positive and end on negative

Explanation: By convention, an electric-field line points in the direction of force on a positive test charge. A positive charge acts as a source, so lines originate from it and generally terminate on negative charges or extend to infinity. Therefore showing lines ending on a positive charge violates this direction rule, making option A correct. Option B reverses the convention, C falsely says a positive charge has no field, and D incorrectly restricts field lines to conductors.

Correct answer: B. No, because direction is not constant

Explanation: The governing concept is that electric field is a vector quantity, represented by both magnitude and direction. A steady uniform electric field must have unchanged magnitude and unchanged direction throughout the relevant region and time. Here, only the magnitude remains constant, while the direction changes with time. Therefore it is not steady uniform. Option A ignores direction, C is conceptually false, and D wrongly denies the vector nature of field.

Correct answer: A. A negative charge is inside the surface

Explanation: Electric field lines are defined to point in the direction of force on a positive test charge. They emerge from positive charges and enter or terminate on negative charges. Hence, when lines cross a closed surface inward, the enclosed source is negative, or the net enclosed charge is negative in a more general situation. Option B and D reverse the direction, while C incorrectly treats a valid field-line pattern as an error.

Correct answer: A. Same magnitude toward the left

Explanation: The governing relation is F = qE. A positive charge experiencing a force to the right tells us that the electric field at the point is directed to the right. Replacing it with an equal-magnitude negative charge reverses the force direction because q is negative, while |q| and E remain unchanged. Therefore, the force has the same magnitude but acts to the left. Hence option A is correct; option B ignores charge sign, C changes magnitude without cause, and D is false.

Correct answer: A. Normally outward everywhere

Explanation: The electric field of an isolated positive point charge is radial and directed outward, described by E = kQ/r^2 in the radial direction. At every point on a sphere centered on the charge, the radius from the centre is normal to the spherical surface. Consequently, the field lines cross the surface normally and outward everywhere. Option A is correct. Tangential or inward lines contradict the radial direction, and the lines meet the whole sphere rather than only one point.

Correct answer: A. Uniformly accelerated motion along the field

Explanation: For a charge q in a uniform electric field E, the electric force is F = qE. Since q and E are constant, the force is constant, and Newton's law gives a = F/m = qE/m, also constant. A positive charge has q > 0, so its acceleration is in the field direction. Released from rest, its speed increases in that direction, giving uniformly accelerated straight-line motion. Option A is correct; no magnetic force or opposing force is specified.

Correct answer: A. Opposite to the electric field

Explanation: The electric force on a charge is F = qE, and acceleration is a = F/m. An electron has charge q = -e, so its force is F = -eE, directed opposite to the electric field. Because its mass is positive, acceleration has the same direction as the force, hence opposite to E. Releasing it from rest changes its subsequent speed but not the initial acceleration direction. Option A is correct; B applies to a positive charge, while C and D contradict F = qE.

Correct answer: A. Electric field would have two directions at one point

Explanation: The tangent to an electric field line at any point represents the direction of the electric field there. Electric field is a definite vector at a given point, so it cannot simultaneously have two different directions. If two field lines intersected, their tangents at the intersection would imply two field directions, producing a contradiction. Therefore field lines cannot cross. Option A states the contradiction; the other choices concern neither vector direction nor the definition of field lines.