Electric Field and Electric Field Lines

Correct answer: A. Straight, parallel and equally spaced

Explanation: A uniform electric field has the same magnitude and the same direction at every point in a region. To represent an unchanged direction, its field lines are straight and parallel. To represent an unchanged magnitude, the spacing between adjacent lines is equal throughout that region. Therefore option A is correct. Curved or intersecting lines imply changing direction, closed circles are not electric-field lines in this situation, and one line cannot represent the complete field pattern.

Correct answer: A. Vector quantity

Explanation: The governing concept is the vector nature of the electric field. At any point, the field is specified by both its magnitude and its direction; its direction is the direction of force on a positive test charge. A physical quantity with both magnitude and direction is a vector. Therefore option A is correct. A scalar has magnitude only, and the remaining choices do not correctly classify a measurable physical field.

Correct answer: A. Newton per coulomb

Explanation: Electric field is defined as force per unit positive charge: E = F/q. Force is measured in newtons (N), and electric charge is measured in coulombs (C). Dividing the units gives N/C, or newton per coulomb, so option A is correct. Joule per coulomb is the unit of electric potential, while C/N and C m are not the usual units of electric field. The equivalent SI form is volt per metre.

Correct answer: A. To the right

Explanation: Electric field direction is defined as the direction of the electric force on a positive test charge. Since the stated test charge is positive and the force on it points to the right, the electric field at that location must also point to the right. No sign reversal is needed. A negative test charge would experience force opposite to the field, but that is not the situation here; therefore option A is correct.

Correct answer: A. Zero

Explanation: The governing relation between electric force and electric field is F = qE. For a small positive test charge q, if the net electric field E at its location is zero, then F = q × 0 = 0. This means the vector sum of electrical forces from all sources is zero, even though individual forces might exist and cancel. Hence option A is correct; the other choices assert a nonzero magnitude or an unjustified direction.

Correct answer: A. Direction of electric field

Explanation: A field line is constructed so that its tangent at any point gives the local direction of the electric field. Thus, for a curved line, drawing a tangent at the chosen point tells us the direction in which a positive test charge would be pushed there. The tangent does not specify the charge's mass, temperature, or magnetic-field magnitude. Therefore option A is correct and is especially useful when interpreting curved electric-field diagrams.

Correct answer: A. Closed loops

Explanation: The governing concept is the standard property of electrostatic field lines. They originate at positive charges and terminate at negative charges or at infinity, and two field lines cannot intersect because the electric field at one point has only one definite direction. They do not form closed loops. Closed-loop lines are associated with a conservative-curl-free electrostatic field being represented differently from magnetic field lines, which form closed loops. Therefore, option A is correct; options B, C, and D describe valid properties.

Correct answer: A. They bend away from each other

Explanation: The governing concept is the field pattern produced by like charges. Both positive charges repel a positive test charge in the region between them, so the resultant field lines curve away from the central region and do not join one charge directly to the other. Field lines also never intersect, because that would imply two electric-field directions at one point. Thus option A is correct. Option B suits the general direction between unlike charges, while C and D contradict field-line rules.

Correct answer: A. From positive charge to negative charge

Explanation: The governing convention for electric field lines is that their arrow direction is the direction of force on a small positive test charge. A positive source charge repels such a test charge, while a negative charge attracts it. Consequently, for an isolated positive-negative pair, the lines are drawn from the positive charge toward the negative charge. Therefore option A is correct. Option B reverses the convention, C describes two positive charges, and D is not an electrostatic field-line pattern.

Correct answer: A. Weak

Explanation: The governing concept is the graphical representation of electric-field magnitude by line density. When the same scale is used, closely packed field lines indicate a stronger field, whereas widely separated lines indicate fewer lines per unit area and therefore a weaker field. Hence option A is correct. Widely spaced lines do not mean that the field is necessarily zero; they only indicate that its magnitude is relatively small in that region. Options B and C describe the opposite or an impossible conclusion.

Correct answer: A. It decreases

Explanation: For a point charge, the electric-field magnitude is given by E = k|Q|/r², where k is Coulomb’s constant, Q is the charge, and r is the distance from it. If r increases while Q remains fixed, the denominator r² becomes larger, so E decreases according to the inverse-square law. Therefore option A is correct. It does not increase or remain constant; for example, doubling the distance reduces the field to one-fourth of its original value.

Correct answer: A. So that it does not disturb the original field

Explanation: The governing concept is the operational definition of electric field: E = F/q, where a small positive test charge is used to measure the force at a point. The charge must be sufficiently small so that its own electric field and the force it produces do not rearrange nearby source charges or significantly alter the original field. Thus option A is correct. Small size does not make it colourless, permanently fixed, or massless, so B, C, and D are irrelevant.

Correct answer: A. Imaginary helping lines

Explanation: The governing concept is the field-line model used to visualize an invisible vector field. Electric field lines are imaginary curves drawn so that their tangent gives the field direction and their relative density represents field strength. They are not material threads, light rays, or sound waves, and no physical object travels along them merely because they are drawn. Therefore option A is correct. The diagram is a useful representation of the field, not a collection of tangible lines.

Correct answer: A. Direction of electric field

Explanation: The governing concept is the directional meaning of electric field lines. At any point, the arrow on a field line indicates the direction of the electric field, which is also the direction of force on a positive test charge placed there. The arrow does not specify the magnitude or physical size of the source charge, nor does it describe paper or time. Therefore option A is correct. Field-line spacing, rather than arrow direction, is used qualitatively to represent field strength.

Correct answer: A. Decreasing

Explanation: The density or spacing of electric field lines represents the relative magnitude of the electric field. Closely packed lines indicate a stronger field, whereas widely separated lines indicate a weaker field. Therefore, when the lines spread from close spacing to wider spacing, the field strength decreases. Option B reverses this relationship, while C ignores the change in spacing and D has no physical basis.

Correct answer: A. Opposite direction

Explanation: Electric field direction is defined as the direction of force on a small positive test charge. The electric force is given by F = qE. For a negative charge, q is negative, so the force vector is opposite to the electric-field vector. Thus option A is correct. Option B applies to a positive charge, whereas C and D are not generally true because direction depends on the field.

Correct answer: A. They originate from a positive charge

Explanation: Electric field lines are an illustrative representation of the electric field. By convention, they originate from positive charges and point away from them; they terminate on negative charges or may extend to infinity if no opposite charge is present. Therefore option A is correct. Option B describes the usual behavior near a negative charge, while C and D contradict the standard field-line pattern.

Correct answer: A. They terminate on a negative charge

Explanation: Electric field lines show the direction in which a positive test charge would move. Since a negative charge attracts a positive test charge, the lines point toward the negative charge and terminate on it. Hence option A is correct. Lines generally originate from positive charges and end on negative charges, although isolated diagrams may show them extending to or from infinity. Options B, C and D are incorrect generalizations.

Correct answer: A. Force will be greater

Explanation: The electric force on a charge is related to the field by F = qE. For the same positive test charge, q remains constant and positive, so increasing the electric-field magnitude increases the force magnitude in direct proportion. Therefore option A is correct. A weaker field would produce a smaller force, not a stronger one; the force is not zero unless the field is zero, and its direction is defined by the field.

Correct answer: A. Smaller electric field

Explanation: In a field-line diagram, the number of lines crossing a unit area is used to represent relative field magnitude. Lines that are close together indicate a strong field, while greater separation indicates a weaker field in that region. Therefore option A is correct. Wider spacing does not imply two field directions, and it does not prove that the charge everywhere is zero; the diagram only gives local field information.

Correct answer: A. Downward

Explanation: The arrow on an electric field line gives the direction of the electric field at that location. Electric force is F = qE, and for a positive charge q is positive, so the force has the same direction as the field. Since the arrows point downward, the force is downward and option A is correct. The opposite direction would apply to a negative charge; the horizontal choices do not follow the stated field direction.

Correct answer: A. Downward

Explanation: Field-line arrows indicate that the electric field is upward. Using F = qE, a negative value of q reverses the force direction relative to E. Consequently, a negative charge experiences a downward force, so option A is correct. A force upward would be appropriate for a positive charge, while the force is not necessarily zero and the horizontal direction is unsupported by the given field.

Correct answer: A. To understand direction and strength of electric field

Explanation: Electric field lines are an imaginary graphical tool used to visualize an otherwise invisible electric field. The tangent to a line gives the field direction, and the relative density or spacing of lines indicates the field strength. Therefore option A correctly states their main use. They are not instruments for measuring sound, changing temperature, or reducing mass; those choices refer to unrelated physical quantities or effects.

Correct answer: A. Uniform electric field

Explanation: Parallel field lines indicate that the electric-field direction is the same throughout the region. Equal spacing indicates that their density, and therefore the field magnitude, is also constant. Together these features define a uniform electric field, so option A is correct. A non-uniform field would show changing direction or spacing; a zero field would have no field lines, and circular lines do not represent the stated parallel pattern.

Correct answer: A. More crowded

Explanation: The electric field due to a point charge has magnitude E = k|q|/r², so it becomes stronger as the distance r decreases. By convention, the density of drawn field lines represents field strength; therefore, lines are shown more closely packed near the charge. Option B represents a weaker distant field, while C and D contradict the basic properties of electrostatic field lines.