Electric Field and Electric Field Lines

Correct answer: A. They cut equipotential surfaces perpendicularly

Explanation: An equipotential surface has the same electric potential at every point, so moving a test charge along it requires no work. The electric field points in the direction of the greatest decrease of potential and therefore has no tangential component on that surface. It must be normal to the surface, so field lines intersect it perpendicularly. Option A is correct.

Correct answer: A. From the positive charge to the negative charge

Explanation: By definition, the direction of an electric field is the direction of force on a small positive test charge. Electric field lines originate at a positive charge and terminate at a negative charge. Thus, for an electric dipole, the external field lines generally run from the positive charge to the negative charge. They do not form closed circles, so option A is correct.

Correct answer: A. To disturb the original field as little as possible

Explanation: Electric field at a point is defined using the force on a positive test charge, but the measuring charge should not significantly alter the source-charge arrangement. Choosing it to be very small keeps its own effect and the disturbance of the original field negligible. The purpose is not to create a large force or destroy charges. Hence option A is correct.

Correct answer: A. Electric field = force divided by test charge

Explanation: The magnitude of electric field is defined as the force experienced per unit positive test charge: E = F/q. Therefore, if the force is known and the test charge is known, dividing F by q gives the field magnitude. Its SI unit is newton per coulomb, equivalent to volt per metre. Thus option A is correct.

Correct answer: A. 5 newtons per coulomb

Explanation: Electric field is defined as force per unit positive test charge: E = F/q. Substituting F = 10 N and q = 2 C gives E = 10/2 = 5 N/C. Because the question asks for magnitude, only the positive numerical value is needed. Option A is therefore correct. Multiplying force and charge would give the wrong units, while options B and D result from failing to divide correctly.

Correct answer: A. 4 newton per coulomb

Explanation: The governing definition of electric field is E = F/q, where F is the force on a small positive test charge and q is its charge. Substituting the given values gives E = 4 N ÷ 1 C = 4 N/C. Therefore, option A is correct. Option B incorrectly uses the charge value, option C reverses the division, and option D doubles the force without any physical reason.

Correct answer: A. It will remain the same everywhere

Explanation: In a uniform electric field, both the magnitude and direction of the field are constant throughout the stated region. The force on a charge is given by F = qE. Since the charge q is unchanged and E is also unchanged, the force remains constant in magnitude and direction. Thus option A is correct; it is not automatically zero, changing, or restricted to a centre.

Correct answer: A. To show the direction of the electric field

Explanation: The arrows on electric field lines represent the direction of the electric field at each point. By definition, this is the direction in which a positive test charge would experience force. Hence option A is correct. The arrow does not measure the line's length, the charge's weight, or artistic appearance. Line density may indicate field strength, but arrow direction indicates field direction.

Correct answer: A. In a uniform electric field

Explanation: Straight, parallel, and equally spaced field lines represent a uniform electric field: the direction is constant because the lines remain parallel, and the magnitude is constant because their spacing is equal. Therefore option A is correct. A point charge produces radial lines, while two charges or an irregular distribution generally produce curved, nonuniform patterns rather than a uniform set.

Correct answer: A. Radially outward

Explanation: A point charge produces a spherically symmetric electric field, so its field lines are directed along radii from the charge. Because a positive charge repels a positive test charge, the force and field point away from the charge in every direction. Thus option A is correct. Inward radial lines describe a negative charge, parallel lines describe a uniform field, and closed squares are not electric field lines.

Correct answer: A. Radially inward

Explanation: Electric field direction is defined as the direction of force on a positive test charge. A negative point charge attracts that test charge, so the field points toward the negative charge from every direction. The lines are therefore radial and inward, making option A correct. Radially outward lines belong to a positive point charge; a single point charge does not create only upward parallel or circular electric field lines.

Correct answer: A. The electric field may be considered zero there

Explanation: In a field-line diagram, the presence and density of lines are used to represent the electric field. If a region is intentionally shown without any field lines, the usual interpretation is that the electric field there is zero or negligible, so option A is correct. A strong field would normally be represented by many closely spaced lines. Absence of lines alone does not prove that only negative charge is present.

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

Explanation: Electrostatic field lines begin on positive charges and end on negative charges, or extend to or from infinity when the corresponding charge is absent. They do not return to their starting point because the electrostatic field is conservative and has zero circulation around a closed path. Therefore option A gives the correct physical description. Closed field-line loops are characteristic of magnetic fields, not electrostatic fields.

Correct answer: A. Direction of force on a positive test charge

Explanation: The arrow direction of an electric field line is defined as the direction of force that would act on a small positive test charge placed at that point. Thus option A is correct. The arrows do not provide the charge's colour, the mass of an object, or any information about the flow of time. Field-line spacing can provide qualitative information about field magnitude, but direction specifically gives the force direction on a positive test charge.

Correct answer: A. From positive charge to negative charge

Explanation: By convention, electric field lines originate on positive charges and terminate on negative charges. Between two opposite charges, the field-line direction is therefore from the positive charge toward the negative charge, making option A correct. Option B reverses the electric-field convention. Lines do not point away from both charges, and they do enter the negative charge rather than avoiding both charges.

Correct answer: A. Field is becoming stronger

Explanation: The density or spacing of electric field lines represents the relative magnitude of the electric field. When the lines become closer, more lines pass through the same region, so the field magnitude is greater there. Therefore, option A is correct. Closer spacing does not mean that the field disappears, that charge changes into mass, or that direction becomes meaningless; arrows still show the field direction.

Correct answer: A. Field is becoming weaker

Explanation: Electric field-line diagrams use line density to show relative field magnitude. As the lines spread farther apart, fewer lines are represented in a given area, indicating a smaller electric-field magnitude. Thus option A is correct. Closer lines would indicate a stronger field; spreading does not erase the field direction, and it does not prove that the source charge is increasing.

Correct answer: A. Positive charge

Explanation: The electric field direction is defined as the direction of force on a positive test charge. This also follows from the relation F = qE: for q > 0, the force vector has the same direction as E. Therefore option A is correct. A negative charge experiences force opposite to E, while a neutron or neutral particle has no electric force due to q = 0 in this idealized context.

Correct answer: A. Negative charge

Explanation: The force on a charge in an electric field is given by the vector equation F = qE. For a negative charge, q is less than zero, so multiplying E by q reverses the direction of the force. Hence option A is correct. A positive charge is pushed along the field, whereas a neutral particle has no electric force from this relation because its net charge is zero.

Correct answer: A. On positive charge

Explanation: By convention, an electric field line points in the direction of force on a positive test charge. Outside an electrostatic charge distribution, lines emerge from positive charges and terminate on negative charges or at infinity. Therefore option A is correct. Negative charges are possible endpoints, while a conductor’s interior is not the universal starting location and a zero-field region cannot define a line direction.

Correct answer: A. On negative charge

Explanation: Electric field lines are conventionally directed from positive charge toward negative charge. Thus a line may terminate on a negative charge, or it may extend to infinity if no opposite charge is present. Option A is correct. A positive charge is normally a source of lines, empty space is not necessarily an endpoint, and magnets belong to magnetic-field diagrams rather than electrostatic field-line diagrams.

Correct answer: A. To the right

Explanation: The arrow placed on an electric field line defines the local direction of the electric field, namely the direction in which a positive test charge would be pushed. Since every parallel line is directed to the right, the field direction is to the right. Therefore option A is correct. The parallel arrangement also suggests a uniform direction, while the other directions contradict the shown arrows.

Correct answer: A. Understanding the direction and relative strength of the electric field

Explanation: Electric field lines are a visual representation, not physical wires. Their arrows show the direction of the electric field, and their relative density indicates the field’s relative strength: crowded lines mean stronger field and widely spaced lines mean weaker field. Hence option A is correct. They do not measure charge colour, calculate time, or convert mass into charge.

Correct answer: A. Away from the positive charge

Explanation: The electric field at a point is defined as the force that would act on a small positive test charge placed at that point, divided by the test charge. A positive source charge repels a positive test charge, so the force and hence the electric-field direction are radially outward, away from the source. The direction is not automatically upward or downward; it depends on the source position. Therefore A is correct.

Correct answer: B. Towards the charge

Explanation: Electric-field lines are drawn in the direction of the force on a positive test charge. A negative source charge attracts such a test charge, so the field vector points toward the negative charge and the lines terminate on it. By convention, lines originate from positive charges and end on negative charges; electrostatic field lines are not closed circular paths. Hence option B is correct, while A reverses the direction and C and D have no valid basis.