4.2.3 Electromotive force and potential difference (3)
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1.
A battery has an e.m.f. of 12V. Explain, using the definition of e.m.f., what this value signifies about the work done on a charge as it moves through the circuit connected to the battery.
An e.m.f. of 12V signifies that the battery performs 12 Joules of electrical work for every Coulomb of positive charge that completes a circuit through the battery. In simpler terms, the battery provides a certain amount of energy per unit charge to push the electrons through the circuit. The 12V value indicates the magnitude of this work done per unit charge. A higher e.m.f. means more work is done on the charge.
2.
Define potential difference (p.d.) in terms of the work done by a unit charge passing through a component. Explain the units used to measure potential difference.
Definition: Potential difference (p.d.) is defined as the work done per unit charge when a charge moves between two points in an electric circuit. More formally, it is the work done (W) by a unit positive charge (q) moving between two points. This can be expressed as: V = W/q.
Units: The SI unit of potential difference is the volt (V). The volt is equivalent to joules per coulomb (J/C), meaning that 1 volt is the energy required to move 1 joule of charge through a 1 coulomb potential difference.
3.
A battery has a potential difference of 12 volts. A current of 2 amps flows through a resistor connected to the battery. Calculate the power dissipated by the resistor. Explain how the potential difference relates to the current and power in a circuit.
Calculation: Power (P) is calculated using the formula P = VI, where V is the potential difference and I is the current. Therefore, P = 12 V * 2 A = 24 watts.
Relationship: The potential difference provides the 'driving force' that causes charges (current) to flow through a circuit. The higher the potential difference, the greater the force on the charges, and thus the larger the current. Power is the rate at which energy is dissipated. It is directly proportional to both the potential difference and the current. A higher potential difference or a higher current will result in a higher power dissipation.