电阻公式
当电压施加在任何导体上时，电荷开始流过导体，电荷的流动速率称为电流。在那里，测量有多少电荷流过它的材料的特性被称为电阻，并且在此基础上，材料被分类为好的或坏的电导体。
电阻
电阻是使用的特性，我们产生热量并在日常生活中有各种应用。
电阻：电导体抵抗（抵抗）电流流动的特性称为电阻。所有材料都有自己的电阻。用R表示，SI 单位为Ohm Ω （希腊字母 Omega）
Georg Simon Ohm was a German physicist who gave a law which is known as ohm’s law and also gives the relation between current, voltage and resistance. According to Ohm’s law, the current flowing through a conductor is directly proportional to the potential difference across it.
V ∝ I
or
V = IR
Therefore, from the above equations, we get the relation:
R = V/I
where,
- V is the potential difference across the conductor (in Volts),
- I is the current through the conductor (in Amperes) and
- R is the constant of proportionality called Resistance (in Ohms).
比电阻（电阻率）
比电阻或电阻率是衡量材料抵抗电流强度的基本属性。低电阻率表示材料容易允许电流。电阻率定义为材料在单位截面上每单位长度提供的电阻，与电阻成反比。
- 电阻率通常用希腊字母 ρ (rho) 表示。
- 电阻率的 SI 单位是欧姆表 (Ω-m) 或 mho。
Mathematically, resistivity is defined as,
ρ = (R×A)/L
or
R = (ρ×L)/A
where
- R is the Resistance,
- L is the Length and
- A is the cross-sectional area of the conductor.
从上述关系可以看出，导体的电阻取决于以下因素：
- 导体截面积
- 导体长度
- 导体材料
- 导电材料的温度
电阻率低的材料是导体，而绝缘体的电阻率比导体的电阻率高。某些材料及其在 20° 时的标准电阻率 (Resistivity) C： Material Resistivity (in Ω-m) Aluminium 2.8 × 10-8 Copper 1.7 × 10-8 Gold 2.4 × 10-8 Carbon (Graphite) 1 × 10-5 Germanium 4.6 × 10-1 Iron 1.0 × 10-7 Lead 1.9 × 10-7 Nichrome 1.1 × 10-6 Silver 1.6 × 10-8
Hence, the two important formulae for Electrical Resistance are as follows:
- R = V/I
- R = (ρ×L)/A
where, R is the Resistance, V is the Voltage, I is the current, ρ is the resistivity, L is the Length and A is the cross-sectional area of the conductor.
电阻问题示例
问题 1：施加电压为 12 V 且流过电流为 4 A 的电路的电阻是多少？
解决方案：
According to the relation:
V = IR
or
R = V/I
Therefore,
R = 12 V/4 A
R= 3 Ω
问题 2： 施加电压为 12 V 且导体电阻为 3 欧姆的电路中流过的电流是多少？
解决方案：
According to the relation:
V = IR
or
I = V/R
This implies,
I = 12 V/3 Ω
I = 4 A
问题 3：通过导体的电流为 4 A 且导体电阻为 3 Ω 的电路施加的电压是多少？
解决方案：
According to the relation:
V = IR
Therefore,
V = 4 A × 3 Ω
V =12 V
问题4：计算长度为4 m、横截面积为10 -6 m 2的铜线的电阻。铜的电阻率为1.7 × 10 -8 Ωm。
解决方案：
Using formula
R = (ρ×L)/A
R = (1.7 x 10-8 Ωm) × 4 m/10-6 m2
R = 6.8×10-2 Ω
问题 5：长度为 4 m、横截面积为 10 -6 m 2的铜线的电阻为 6.8 × 10 -2 ohms。计算铜的电阻率。
解决方案：
Using formula
ρ = (R×A)/L
ρ = (6.8 × 10-2) × 10-6 / 4
ρ = 1.7 × 10-8 Ωm.