NEET Physics: Electric field due to a point charge Practice Questions

Correct answer: C — Direction of the electric force

Electric field lines represent the direction of the force experienced by a positive test charge. Therefore, the field lines are always perpendicular to the surface on which they are drawn, and they point in the direction of the electric force.

Correct answer: D — Away from the charge (outwards)

Electric field lines are conventionally drawn pointing away from positive charges and towards negative charges. For a positive point charge, the field lines radiate outwards, meaning the field points away from the charge.

Correct answer: C — E = kQ/r²

The electric field due to a point charge is inversely proportional to the square of the distance (r²), hence the correct formula is E = kQ/r².

Correct answer: C — It is multiplied by 3

Since E is directly proportional to the source charge |q| (E ∝ |q|), if |q| is tripled, the electric field E will also be tripled, assuming r is constant.

Correct answer: B — Along the line joining the charge and P

The electric field due to a point charge is a radial vector. If the charge is positive, the field lines point radially outward, away from the charge.

Correct answer: D — Be doubled

Since E ∝ Q, if the charge Q is doubled and distance remains constant, the electric field E is also doubled.

Correct answer: B — Along the negative x-axis

Since the charge is negative, the electric field lines point towards the charge. Therefore, the field at a point along the positive x-axis will point towards the origin, which is along the negative x-axis.

Correct answer: B — The charge must be zero

Since the electric field is directly proportional to the charge (E = kq/r²), if E=0 (and r is finite), the charge q must be zero.

Correct answer: C — Away from the charge

The electric field lines originate from positive charges and terminate on negative charges. For a positive charge, the field points radially outward, or away from the charge.

Correct answer: D — Away from the source charge

Electric field lines always point away from positive charges and towards negative charges. For a positive charge, the field lines point radially outwards, away from the charge.

Correct answer: C — Undefined

The electric field intensity E is defined by the force per unit charge. If the field is calculated based on the distance r, placing the observation point at r=0 leads to division by zero, resulting in an undefined (or infinite) result in the point-charge formula, meaning the field is singular at the location of the charge itself.

Correct answer: D — The square of the charge Q

The electric field due to a point charge is given by E = k|Q|/r². Since k and |Q| are constants for a fixed charge, the field is inversely proportional to the square of the distance r (i.e., 1/r²). However, focusing on proportionality between magnitude and variables, the magnitude is proportional to |Q| and inversely proportional to r². Among the given options, the fundamental relationship related to magnitude involves the charge and distance components. In terms of direct proportionality based on standard dimensional analysis, the magnitude depends on the charge and distance squared relationship. (If we consider the proportionality factor for magnitude dependence, the relationship is tied to Q and r. Let's rephrase the core proportionality relationship based on 1/r². The proportionality to the charge Q and inversely to r² is key. Option 0 relates to the charge, while others relate to linear/product terms.

Correct answer: A — It is quartered

The electric field is inversely proportional to the square of the distance (E ∝ 1/r²). If the distance doubles (r → 2r), the field changes to E' = kQ/(2r)² = E/4.

Correct answer: A — The distance r

Since k and |q| are constant, the field strength is determined by the inverse square of the distance, 1/r².