Static Electricity on metal sphere

AI Thread Summary
The discussion revolves around the behavior of a metal-coated sphere when brought near a negatively charged rod. As the sphere approaches, free electrons in the sphere move away from the rod due to repulsion, while positive charges are attracted towards the rod, leading to a redistribution of charge on the sphere. The sphere, despite being initially uncharged, experiences an attraction to the rod because of this charge separation. Participants also discuss the need for clarity in the homework question and the importance of understanding electrostatic principles. Overall, the interaction illustrates fundamental concepts of electrostatics, including charge movement and attraction.
DarkPhoenix
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(b) An uncharged metal-coated sphere hangs from an insulating thread. The sphere is brought
near to the rod. The sphere is attracted to the rod, as shown in Fig. 11.1.

(i) Describe and explain what happens to the free electrons in the metal-coated sphere as it
approaches the rod.
(ii) Draw a diagram to show how charge is distributed on the sphere.
(iii) Explain why the uncharged sphere is attracted to the negatively-charged rod.

(d) Describe one device where electrostatic charging is used. In your answer include a
diagram and explain how and why the charge is produced.
 
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Hi DarkPhoenix! :smile:
DarkPhoenix said:

The Attempt at a Solution



(b)(i) Electrons move towards the right since like charges repel.
(ii) Unlike Charges attract. Thus, positive charges from sphere are attracted to rod.

(i) Yes. :smile:

(ii) ah, but surely the negative charges from the sphere are repelled from the rod; and there are an equal number of positive and negative charges; so why doesn't all the attraction and repulsion cancel out? :wink:
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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