Electric charges and fields

Two students Aditi and Ishaan are sitting at the ends of a straight line. Another student Anika is placed at the midpoint of the line. Then the student Anika placed at the midpoint will: 

• lie at rest

• move towards the bigger student

• move towards smaller student and then come to rest

• move towards the bigger student and then come to rest.

A charge q is placed at the center of the line joining the two equal charges Q. This system of three charges will be in equilibrium if q is equal to:

• - Q/2

• – Q/4

• Q/4

• Q/2

A student named Kabir is studying the interaction between charges. He observes that a charge q1 exerts some force on a second charge q2. A third charge q3 is brought near. Then, the force exerted by q1 and q2 will:

• decrease in magnitude

• increase in magnitude

• remain unchanged

• increase, if q2 is of the same sign as q1 and will decrease, if q2 is of opposite sign.

Five students named Kiara, Shreya, Naira, Aarav, and Arjun are participating in a science experiment. Pairs (Kiara, Shreya), (Shreya, Aarav), and (Aarav, Kiara) show strong friendship, while pairs (Shreya, Naira) and (Aarav, Arjun) have conflicts. Therefore, Kiara must be:

• best friends with Shreya

• enemies with Naira

• neutral towards Aarav

• related to Arjun

Answer explanation

Ball 1 must be neutral because it is involved in both attraction and repulsion with other balls, indicating no net charge.

Three charges +4q, Q and q are placed in a straight line of length l at points distance O, l/2 and l, respectively. What should be Q in order to make the net force on q to be zero?

• -q

• -2q

• – q/2

• 4q. 

Four students are sitting at the corners of a square classroom [as shown in the figure]. The teacher asks a question, and the correct answer is with the student sitting at the centre of the classroom. What is the force on the student at the centre?

• along the diagonal AC

• along the diagonal BD

• perpendicular to the side AB

• zero. 

A small metal ball is suspended in a uniform electric field with the help of an insulated thread. If high energy X-ray beam falls on: 

• the ball will be deflected in the direction of field  

   

• the ball will be deflected opposite to the direction of field

• the ball will not deflect at all

• the ball will fly to infinity.

Answer explanation

The small metal ball will be deflected in the direction of the electric field when high energy X-ray beam falls on it due to the interaction between the electric field and the charged ball.

Three charges each of +q are placed at the three vertices of an equilateral triangle. If the distance of centroid from each vertex of the triangle is r, then strength of electric field at the centroid will be:

• zero

Two fixed point charges +4q and +q units are separated by a distance a. The point, where the resultant field intensity is zero is: 

• 2/3 a

• ½ a

• 3/2 a

• None of these.

Three students Tisha, Divya, and Nikita are participating in a science experiment. They are representing point charges +4q, -q, and +4q respectively, placed on the X-axis at points x = 0 and x = 2a. Which of the following statements is true about their equilibrium?

• Tisha is the only one in stable equilibrium.

• None of the students are in unstable equilibrium.

• All three students are in unstable equilibrium.

• All three students are in stable equilibrium.