1. when their charges are of the same signs
Explanation:
Electrostatic force is the force exerted betwen objects that have charge. The magnitude of the force is given by:
[tex]F=k\frac{q_1 q_2}{r^2}[/tex]
where k is the Coulomb constant, q1 and q2 are the charges of the two objects, and r is the separation between the two objects. The sign (and therefore the direction) of the force depends on the relative signs of the two charges. In fact:
- When the two charges have same sign, the force is positive, which means that it is a repulsive force
- When the two charges have opposite sign, the force is negative, which means that it is an attractive force
So, we can conclude that
Two charged objects repel each other when their charges are of the same signs
2. Two terminals, one positive and negative
Explanation:
Batteries are devices which provides (usually through some chemical reactions) a potential difference, also called electromotive force. When connected to a closed circuit, this potential difference provided by the battery "pushes" electrons through the circuit, generating an electric current.
Batteries have generally two terminals: one terminal at positive voltage, called positive terminal, and one terminal at negative voltage, called negative terminal. When connected to the circuit, electrons are pushed from the negative terminal through the circuit towards the positive terminal of the battery.
