If two objects attract each other, we cannot conclude that both of the objects have charges. Example : A negatively charged plastic stick and neutral pieces of paper. However, if two objects were to repel each other, we can conclude that they have like charges. Conservation of Charge When electrons are transferred from one material to another, none are created or destroyed. Coulomb’s Law: Calculates the force of attraction/repulsion between two charges. F e = (kq 1 q 2 )/d^2
q 1 and q 2 are values of 2 charges which are separated by a distance “d” meters. They equal to the electric force of attraction (F e ). k is the constant, and it will always equal to 9 x 10^9 . ● They have opposite direction ● They have the same value/magnitude ● Both these forces have equal values and opposite direction. ● This forms an Action-Reaction pair because this is happening on two different objects. If q 1 were to increase by a factor of 10, by what factor does the following force values change? A. The force due to q 1 on q 2 changes by a factor of 10 . B. The force due to q 2 on q 1 changes by a factor of 10 . See that only one force has changed, but it affected both of them. If I doubled the distance, the force of attraction will reduced by 4 times . Gravitational forces are only attractive, and Electrical forces may be either attractive or repulsive. ● Both can act between things that are not in contact with each other ● Gravitational forces act in a straight-line direction between masses, and electrical forces act in a straight-line direction between charges. ● A force field surrounds any mass (gravitational field), and any charged object (electric field). Charge Polarization: distortion of charge in the atom or molecule is electric polarization . Molecules can’t move from their relatively stationary positions, but their “centers of charge” can move. This happens when there is a change in distribution which vanishes when external charge is absent or removed. How does a charge affect its surrounding region? Through a property called an electric field . Electric field around a single positive charge. If you place a positive test charge, it will repel because the test charge and that single positive charge are like charges, leading the test charge to run away from the single positive charge. Electric field is a vector quantity. Electric field lines are imaginary lines (with direction) that are drawn around charges, and they demonstrate/held in visualizing the effect of a charge on its surrounding. A test charge always moves along the electric field lines; in the same direction as the electric field lines. Bunched together -> field is strongest Lines further apart -> field is weaker Electric Dipole is a 2 charge system in which two charges of opposite signs are separated by some distance. The direction of an electric field, by convention, is the direction of force that the field would exert on a proton . Electric Conductors are materials that allow charged particles to pass through them easily. Atoms of metals have free electrons that conduct through a metallic conductor when a potential difference exists. The result is an electric current.
- Spring '14