Electrostatic Force Forces on Charged Objects An electroscope

Electrostatic Force

Forces on Charged Objects • An electroscope consists of a metal knob connected by a metal stem to two thin, lightweight pieces of metal foil, called leaves. • Electroscopes are sensitive and useful for determining electric charge.

Forces on Charged Objects The figure on the right shows a neutral electroscope. Note that the leaves hang loosely and are enclosed to eliminate stray air currents.

Forces on Charged Objects • Charging a neutral object by touching it with a charged object is called charging by conduction. • When a negatively charged rod is touched to the knob of an electroscope, electrons are added to the electroscope. • As shown in the figure, the two leaves are charged negatively and repel each other; therefore, they spread apart.

Forces on Charged Objects • The type of charge carried by an electroscope can be determined by observing the leaves when a rod of known charge is brought close to the knob.

Forces on Charged Objects • The leaves will spread farther apart if the rod and the electroscope have the same charge. • The leaves will fall slightly if the electroscope’s charge is opposite that of the rod.

Forces on Charged Objects The process of charging a neutral object by bringing a charged object near it is called charging by induction.

• Happens when charged object is brought near but does not touch a neutral object • Only negative charge (electrons) can flow • When charged object is brought near a conductor, the – charge in the conductor will either be attracted or repelled by the charged object

Forces on Charged Objects The process of removing excess charge by connecting an object to Earth is called grounding.

• Highly charged conductors induce charges in nearby objects • Electrons are strongly attracted to induced opposite charge even if a gap exists between them • Spark is when electrons jump across the gap • Sparking effect can be magnified by changing the shape of the conductor to a sharp point – this concentrates charge at a point