# IGCSE：Circult 快速复习

## Table

Concept | Formula | Symbol |
---|---|---|

Current | I = Q/t | I |

Voltage | V = W/Q | V |

Charge | Q = n x e | Q |

EMF | EMF = W/Q | EMF |

PD | PD = W/Q | PD |

## Cards

Circult 有 5 个基础概念。

### Current (I)

**Definition:**The flow of electric charge through a circuit**Unit:**Amperes (A)**Formula:**I = Q/t**Calculation:**Current is calculated as the rate of flow of electric charge. It is measured in amperes (A). The formula for calculating current is I = Q/t, where I is the current, Q is the electric charge flowing through the circuit, and t is the time taken for the charge to flow.

Practice Question:A circuit has a current of 2 A and a time of 5 s. What is the amount of electric charge that has flowed through the circuit?

### Voltage (V)

**Definition:**The measure of the amount of energy required to move a unit of electric charge from one point in a circuit to another**Unit:**Volts (V)**Formula:**V = W/Q**Calculation:**Voltage is calculated as the amount of energy required to move a unit of electric charge. It is measured in volts (V). The formula for calculating voltage is V = W/Q, where V is the voltage, W is the work done in moving the charge, and Q is the amount of charge moved.

Practice Question:A 6 V battery is used to power a circuit with a resistance of 2 ohms. What is the current flowing through the circuit?

### Charge (Q)

**Definition:**The property of matter that describes the amount of electrical energy contained within an object**Unit:**Coulombs (C)**Formula:**Q = n x e**Calculation:**Charge is calculated by multiplying the number of charged particles by the elementary charge. It is measured in coulombs (C). The formula for calculating charge is Q = n x e, where Q is the electric charge, n is the number of charged particles, and e is the elementary charge (1.6 x 10^-19 C).

Practice Question:What is the amount of electric charge contained in a circuit if there are 3 x 10^19 electrons present?

### Electromotive Force (EMF)

**Definition:**The energy per unit of charge that is converted into electrical energy by an electrical source such as a battery**Unit:**Volts (V)**Formula:**EMF = W/Q**Calculation:**EMF is calculated as the energy per unit of charge that is converted into electrical energy by an electrical source such as a battery. It is measured in volts (V). The formula for calculating EMF is EMF = W/Q, where EMF is the electromotive force, W is the work done by the source in moving the charge, and Q is the amount of charge moved.

Practice Question:A battery has an EMF of 12 V and a resistance of 4 ohms. What is the current flowing through the circuit?

### Potential Difference (PD)

**Definition:**The difference in electric potential energy between two points in a circuit**Unit:**Volts (V)**Formula:**PD = W/Q**Calculation:**PD is calculated as the difference in electric potential energy between two points in a circuit. It is measured in volts (V). The formula for calculating PD is PD = W/Q, where PD is the potential difference, W is the work done in moving the charge between the two points, and Q is the amount of charge moved.

Practice Question:A circuit has a PD of 10 V and a current of 2 A. What is the amount of electric charge that has flowed through the circuit in 5 seconds?

## Full Explain

In physics, a circuit refers to a **closed loop** path that electricity can flow through. A circuit can be made up of different components such as wires, batteries, resistors, capacitors, switches, and bulbs, among others. A circuit can be either series or parallel.

In a **series** circuit, the components are arranged in a line so that the current flows through each component one after the other. In a **parallel** circuit, the components are arranged so that the current can flow through multiple branches simultaneously.

**Current** is the flow of electric charge through a circuit, and is measured in amperes (A). It is defined as the **rate of flow** of electric charge, where 1 ampere of current is equivalent to 1 coulomb of charge flowing through the circuit in 1 second.

**Voltage**, also known as electric potential difference, is a measure of the **amount of energy** required to move a unit of electric charge from one point in a circuit to another. It is measured in volts (V) and is the driving force that causes the electric charge to flow through the circuit.

**Charge** is a property of matter that describes the **amount of electrical energy** contained within an object. It is measured in coulombs (C).

**EMF** (electromotive force) is the **energy per unit of charge** that is converted into electrical energy by an electrical source such as a battery. It is measured in volts (V) and is the driving force that causes current to flow through the circuit.

**PD** (potential difference) is the **difference in electric potential** energy between two points in a circuit. It is measured in volts (V) and is the driving force that causes the electric charge to flow from a higher potential point to a lower potential point in the circuit.

For example, consider a simple circuit consisting of a battery, a bulb, and a switch connected in series. When the switch is closed, the battery provides an EMF that causes the current to flow through the circuit. As the current flows through the bulb, it encounters resistance, which results in a PD across the bulb that causes it to light up.

In summary, a circuit is a closed loop path that allows the flow of electric charge. Current is the **rate** of flow of electric charge, voltage is the driving **force** that causes the electric charge to flow through the circuit, charge is the property of matter that describes the **amount** of electrical energy contained within an object, EMF is the energy **per unit** of charge that is converted into electrical energy by an electrical source, and PD is the **difference** in electric potential energy between two points in a circuit.