Electric Field and Electric Field Lines

Correct answer: A. Force on a unit positive test charge

Explanation: The governing concept is the definition of electric field. At a point, electric field is the electric force experienced per unit positive test charge, expressed as E = F/q. Its direction is the direction of force on a positive test charge. Therefore option A is correct. Force per unit mass defines gravitational field, charge per unit time is current, and force per unit area is pressure.

Correct answer: A. Positive test charge

Explanation: The electric field at a point is defined as the force experienced per unit positive test charge placed at that point, so its direction is the direction of force on a positive test charge. A negative test charge would experience force opposite to the field. A neutron has no charge, and using both proton and electron together is not the defining convention. Therefore, option A is correct.

Correct answer: A. Away from the charge

Explanation: Electric field lines are drawn in the direction in which a positive test charge would move. A positive point charge repels a positive test charge, so the electric field points radially outward from the charge. The lines do not point inward, form circles, or lack direction. Their spacing may change with distance, but their direction remains outward. Hence option A is correct.

Correct answer: A. They go towards the charge

Explanation: The direction of an electric field is defined by the force on a positive test charge. A negative point charge attracts such a test charge, so the field lines point radially inward toward the negative charge. Outward lines describe a positive charge, while parallel lines represent a uniform field and closed circles are not electric field lines. Thus option A is correct.

Correct answer: A. Because field cannot have two directions at one point

Explanation: At every point, the electric field vector has one definite direction, given by the force on a positive test charge. If two electric field lines intersected, their tangents at the intersection would indicate two different field directions at the same point, which is physically impossible. The rule is unrelated to the sign of charge, circular shape, or vacuum. Therefore option A is correct.

Correct answer: A. Electric field is stronger

Explanation: In a field-line diagram, the density of lines represents the relative magnitude of the electric field. When lines are closer together, more lines cross a given area, indicating a stronger field and a larger force on a given positive test charge. This does not mean the field is zero, that its direction reverses, or that charge disappears. Hence option A is correct.

Correct answer: A. By equally spaced parallel straight lines

Explanation: A uniform electric field has the same magnitude and the same direction at every point in the represented region. Therefore, its field lines must be straight and parallel to show constant direction, and equally spaced to show constant magnitude. Curved or irregular lines indicate changing direction or strength, while closed circles do not represent electrostatic field lines. Thus option A is correct.

Correct answer: A. East direction

Explanation: The electric field direction at a point is defined as the direction of force on a positive test charge. Since the stated test charge is positive and the force on it is directed eastward, the electric field at that point is also directed eastward. The field would be opposite to the force only for a negative charge. Therefore, option A is correct.

Correct answer: A. West direction

Explanation: The force on a charge is given by F = qE. For a negative charge, q is negative, so the force direction is opposite to the electric-field direction. The force here points east, therefore the electric field must point west. Choosing east would ignore the negative sign; north and south do not satisfy the stated opposite-direction relation. Hence option A is correct.

Correct answer: A. Direction of electric field at that point

Explanation: An electric field line is constructed so that its tangent at any point gives the direction of the electric field vector there. A small positive test charge would experience force along this tangent, assuming the field is represented without other complications. The tangent does not provide charge colour, mass, or temperature. Therefore, the direction of the electric field is represented by option A.

Correct answer: A. They start from positive charge and end on negative charge

Explanation: By convention, electric field lines point in the direction of force on a positive test charge. They emerge from positive charges and terminate on negative charges, showing repulsion from positive and attraction toward negative charge. For an isolated charge, a line can extend to or come from infinity, so the statement is a general rule for lines connecting charges. Thus option A is correct.

Correct answer: A. In the direction of the electric field

Explanation: The governing relation is F = qE, where E is the electric field and q is the charge. For a positive charge, q is greater than zero, so multiplying E by q preserves the direction of E. Therefore, the force acts along the electric field, making option A correct. Option B applies to a negative charge, while C and D are not generally valid.

Correct answer: A. Opposite to the electric field

Explanation: The electric force is given by F = qE. A negative charge has q less than zero, so the scalar multiplication reverses the direction of the electric-field vector. Hence the force acts opposite to the field, making option A correct. The field does not automatically point upward or downward; those directions depend on the actual arrangement of charges.

Correct answer: A. Because it has both magnitude and direction

Explanation: Electric field is defined as the force experienced per unit positive test charge, E = F/q. Force is a vector, so electric field also has a magnitude and a definite direction. Its direction is the direction of force on a positive test charge. Therefore option A is correct; option B describes a scalar, while C and D are false because electric field can be nonzero and has units N/C.

Correct answer: A. It decreases inversely as the square of distance

Explanation: For a point charge, the electric-field magnitude is E = k|Q|/r². Thus, with the source charge unchanged, increasing r makes the denominator larger and the field decreases as the inverse square of distance. For example, doubling r changes E to E/4. Therefore option A is correct; the other choices use incorrect distance dependences.

Correct answer: A. One-fourth of the original field

Explanation: The electric field due to a point charge follows the inverse-square relation E = k|Q|/r². If the original distance is r, E₁ = k|Q|/r². When the distance becomes 2r, E₂ = k|Q|/(2r)² = k|Q|/(4r²) = E₁/4. Thus the field becomes one-fourth of its original value, so option A is correct. The other choices ignore or reverse the inverse-square dependence.

Correct answer: A. Increasing the magnitude of the source charge

Explanation: For a point source, E = k|Q|/r². If r is fixed, the field strength is directly proportional to the magnitude of the source charge |Q|. Therefore increasing |Q| increases E, so option A is correct. The test charge is used to measure the field and does not determine the source field; colour, time, and naming have no role in this electrostatic relation.

Correct answer: A. Because they are drawn to represent the field

Explanation: An electric field is a real physical effect because it can exert force on a charge and produce measurable consequences. Field lines are not material wires or visible objects; they are an imaginary graphical model used to show the field direction and relative strength. Thus option A is correct. Option B wrongly denies the field, while C and D misunderstand the purpose of the representation.

Correct answer: A. Zero

Explanation: At the midpoint, the two equal positive charges are at equal distances, so each produces an electric field of the same magnitude, E = kQ/r². The field from the left charge points away from it, and the field from the right charge points in the opposite direction. These equal and opposite vectors cancel, giving zero net field. Hence option A is correct.

Correct answer: A. The net field is the vector sum of all individual fields

Explanation: The superposition principle states that each source charge produces its own electric field independently. The resultant field at a point is obtained by adding all individual field vectors: E_net = E₁ + E₂ + E₃ + … . Both magnitudes and directions must be considered, so option A is correct. The net field is not always zero, smallest, or due to only one charge.

Correct answer: A. The net electric force on a positive test charge there will be zero

Explanation: Electric field is defined as force per unit positive test charge, E = F/q. If E is zero at a point, the resultant electric force on a suitably small positive test charge placed there is zero. This can happen because fields from several nearby charges cancel; it does not prove that no charges exist. Therefore option A is correct, while C and D concern unrelated ideas.

Correct answer: A. Indication of the magnitude of charge

Explanation: The number of electric field lines drawn from or toward a charge is conventionally proportional to the magnitude of that charge. A larger positive or negative charge is represented by more lines, showing a stronger field overall. The lines do not represent colour, temperature, or age; those properties have no role in this electrostatic diagram convention. Therefore, option A is correct.

Correct answer: A. Perpendicularly

Explanation: In electrostatic equilibrium, the electric field cannot have a tangential component at a conductor’s surface. If such a component existed, free charges would move along the surface, contradicting equilibrium. Thus the field is normal to the surface, and field lines meet it perpendicularly. They are not generally parallel or oblique, so option A is correct.

Correct answer: A. Where the electric field is stronger

Explanation: The density of electric field lines in a diagram represents the relative magnitude of the electric field. Where lines are closer together, a unit area is crossed by more lines, indicating a stronger field. Widely separated lines indicate a weaker field, while no electric field would have no field lines. Therefore, option A is correct.

Correct answer: A. Weak electric field

Explanation: Field-line spacing is used to compare electric-field strength. Closely packed lines represent a large field magnitude, whereas larger separation means fewer lines per unit area and therefore a weaker field. Spacing does not indicate mass or automatically mean that the charge has doubled. Thus the physically meaningful interpretation is option A, weak electric field.