Electric charge, conservation, Coulomb's law, superposition
- Two identical charged conducting spheres A and B have their centres separated by a certain distance. Charge on each sphere is q and the force of repulsion between them is F. A third identical uncharged conducting sphere is brought in contact with sph… Answer: 4. 3F/8 Key idea: identical conducting spheres share charge equally on contact. Third sphere touches A: A and C each have q/2 . Then... 1
- Two point charges A and B, having charges +Q and -Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes : Answer: 2. 9F/16 25% of A's charge is 0.25Q . After transfer: q_A=0.75Q and q_B=-Q+0.25Q=-0.75Q . Coulomb force F∝ q_Aq_B at the same distan... 1
- Suppose the charge of a proton and an electron differ slightly. One of them is -e, the other is (e+Δ e). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart… Answer: 2. 10⁻³⁷ C Key idea: each hydrogen atom then has a net charge Δ e , and the electric repulsion balances gravity. (Δ e)²/4πε₀d²=Gm_h²... 1
- Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d (d << l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a… Answer: 3. v ∝ x^(-1/2) Key idea: at equilibrium, the electric force balances the horizontal component of tension. With tanθ≈x/2l : kq²/x²=m... 1