Electric Field and Electric Field Lines

Correct answer: A. Low

Explanation: For a point charge, the electric-field magnitude follows E = k|q|/r². As the distance r increases, the field becomes weaker. Since field-line density is used to represent field strength, the lines are drawn farther apart and therefore have lower density far from the charge. Option B is the opposite trend; C is impossible, and D ignores the inverse-square dependence.

Correct answer: A. Along the arrow on the line

Explanation: An electric field line is drawn so that its tangent gives the direction of the electric field at every point. The force on a charge is F = qE. For a positive test charge, q is positive, so the force and its initial acceleration are in the same direction as E, namely along the arrow on the line. A negative charge would move oppositely.

Correct answer: A. Density of field lines

Explanation: Electric-field intensity is a vector quantity, but in a field-line diagram its relative magnitude is represented by the density of lines in a given area. Closely spaced lines indicate a stronger field, whereas widely spaced lines indicate a weaker field. The name of the charge, diagram size, and paper thickness do not measure field intensity, so options B, C, and D are irrelevant.

Correct answer: A. In a uniform field

Explanation: In a uniform electric field, the electric-field vector has the same magnitude and direction at every point. Its field-line representation therefore consists of straight, parallel, equally spaced lines. A point charge produces radial lines, and the region between like charges is generally non-uniform. Thus, options B and C are not generally valid, while D contradicts the definition of a non-uniform field.

Correct answer: A. Indication of larger charge or stronger field

Explanation: Field lines are an illustrative convention: their number and density indicate the strength of the electric influence. For comparable diagrams, a larger charge is represented by more lines emerging from a positive charge or terminating on a negative charge. More lines can also indicate a stronger field in a region. Temperature, mass, and sound are unrelated to this convention, so B, C, and D are distractors.

Correct answer: A. Radially

Explanation: A point charge has spherical symmetry: its electric influence depends only on the distance from the charge, not on the direction. Consequently, field lines are radial. They point outward from a positive charge and inward toward a negative charge. Square, spiral, or purely horizontal patterns do not represent the field of an isolated point charge, so options B, C, and D are incorrect.

Correct answer: A. It increases

Explanation: The electric field magnitude around a point charge is proportional to its magnitude: E = k|q|/r². Increasing a positive charge therefore increases the strength of its electric influence. In a field-line diagram, this is represented by drawing more lines associated with the charge. The lines still point outward because the charge remains positive; they do not decrease, vanish, or reverse direction.

Correct answer: A. Curved

Explanation: The tangent to an electric field line gives the field direction at that point. If the direction changes continuously from one point to another, the tangent must change as well, so the line can be curved. Curvature does not mean that field lines intersect; two lines cannot cross because that would assign two directions to the field at one point. Straight parallel lines describe a uniform field.

Correct answer: A. Two lines must never intersect

Explanation: At any point in space, the electric field has one definite direction, represented by the tangent to the field line there. If two electric field lines intersected, their tangents would give two different directions at the same point, which is impossible. Therefore, field lines never cross. They generally begin on positive charges and end on negative charges or at infinity; they are not necessarily closed circles.

Correct answer: A. Normally

Explanation: In electrostatic equilibrium, charges inside a conductor rearrange themselves until the tangential component of the electric field at its surface becomes zero. Therefore, the remaining electric field is directed along the normal to the surface, so field lines meet it perpendicularly. They cannot be parallel or oblique, because either case would produce a tangential component and move surface charges.

Correct answer: A. Positive test charge

Explanation: Electric field at a point is defined as the force experienced per unit positive test charge placed at that point: E = F/q. The direction of E is therefore the direction of force on a small positive test charge. A negative test charge would experience force in the opposite direction, while a neutral particle or photon does not provide this defining convention.

Correct answer: A. Because like charges repel

Explanation: Like charges exert repulsive forces on one another, so the electric field near them is directed away from both charges and the corresponding lines bend outward rather than joining directly. Field lines may begin on positive charges and end on negative charges or at infinity; they are not generally closed loops. Thus attraction and absence of a field are incorrect explanations.

Correct answer: A. Attraction and direction from positive to negative

Explanation: Electric field lines conventionally originate on positive charges and terminate on negative charges. When lines connect a positive and a negative charge, their direction from positive to negative represents the electric field, and the opposite charges attract one another. The other choices reverse the direction or incorrectly claim that no electrical or only thermal effect exists.

Correct answer: A. Same direction

Explanation: The electric force on a charge is given by F = qE. For a positive charge, q is positive, so the force vector has the same direction as the electric-field vector. A negative charge would reverse the direction because q is negative. The force is not necessarily perpendicular, and it is not unrelated to the field, so option A is correct.

Correct answer: A. Left

Explanation: The arrow on an electric field line indicates the direction of the electric field at that location. By definition, a positive test charge experiences electric force in the same direction as the field, according to F = qE with q > 0. Since the arrow points left, the force is leftward. A negative charge would instead feel a rightward force.

Correct answer: A. Colour of charge

Explanation: Electric field lines are a visual representation of an electric field, not physical objects. Their arrows show field direction, their relative spacing indicates field strength, and they conventionally run from positive toward negative charges or infinity. They do not encode a charge’s colour or visual appearance. Therefore, colour is the information not directly represented.

Correct answer: A. They are imaginary lines used to represent direction and strength of electric field

Explanation: Electric field lines are imaginary graphical constructs used to visualize an electric field. The tangent to a line gives the field direction, while the density or spacing of lines gives a qualitative comparison of field strength. They are not wires, sound paths, or temperature scales, so option A gives the complete and scientifically correct description.

Correct answer: A. The electric field is uniform and directed from left to right

Explanation: Straight, parallel field lines with equal spacing represent a uniform electric field: the direction is constant because the lines are parallel, and the magnitude is constant because their spacing does not change. The arrows specify the direction; with arrows from left to right, the field points rightward. A negative charge cannot emit field lines outward, so the other interpretations are incorrect.

Correct answer: A. Electric field remains the same

Explanation: Electric field at a point is defined as the force experienced per unit positive test charge: E = F/q. Initially, let the field be E = F/q. After the change, the force is 2F and the test charge is 2q, so E' = 2F/2q = F/q = E. The ratio remains unchanged; therefore option A is correct. Doubling only the force or only the charge would give a different result.

Correct answer: B. South direction

Explanation: The electric field direction is defined as the direction of force on a positive test charge. The force on any charge is given by F = qE. Since the placed charge is negative, q is less than zero, so its force is opposite to the electric-field direction. Therefore, an electric field pointing north produces a southward force on this negative charge. Option A would apply to a positive charge, while east and west are unrelated directions.

Correct answer: C. By adding them directly

Explanation: Electric field is a vector quantity, so both magnitude and direction must be considered when combining fields. If two fields point in the same direction, their vectors are parallel and reinforce one another. Thus, if their magnitudes are E₁ and E₂, the resultant magnitude is E = E₁ + E₂ in that common direction. Subtraction is used for opposite directions, multiplication is not the superposition rule, and neither field becomes zero merely because the directions are the same.

Correct answer: B. Zero

Explanation: The governing concept is vector superposition: the net electric field is the vector sum of all individual fields. For two fields with equal magnitude E but opposite directions, one may be represented as +E and the other as −E along the same axis. Therefore, E_net = E + (−E) = 0. A doubled field would result when equal fields point in the same direction, and multiplication is not used to combine electric-field vectors. Hence option B is correct.

Correct answer: B. Field decreases with distance

Explanation: The density of electric-field lines is a visual representation of field strength: a greater number of lines crossing a given area indicates a stronger field. Close to a positive point charge, the lines are crowded, so the field magnitude is large. As distance increases, the lines spread over larger spherical areas and their density decreases; quantitatively, the magnitude follows E = kQ/r². Therefore the field decreases with distance. Line density does not mean the field is zero, and unchanged direction does not imply unchanged magnitude.

Correct answer: A. Because force on a positive test charge is from positive to negative

Explanation: Electric-field direction is defined as the direction of the force on a small positive test charge. A positive test charge is repelled by the positive source charge and attracted by the negative source charge. Consequently, in the region between unlike charges, the force direction and hence the field-line direction is from positive to negative. Negative charges also produce electric fields, so option B is false. The direction is not determined by “downward,” and unlike charges are not identical.

Correct answer: A. So that it disturbs the original electric field very little

Explanation: The electric field at a point is defined using a hypothetical positive test charge as E = F/q. The test charge must be very small so that its own electric field does not significantly rearrange or disturb the source charges producing the original field. Thus the measured force represents the pre-existing field. A small charge does not remove the source charge, make the force zero, or alter the direction rule, so option A is correct.