Which two devices do not obey Ohms law?
2 Answers
Ohm's Law is a fundamental principle in electrical engineering and physics that states the relationship between voltage (V), current (I), and resistance (R) in a circuit: \( V = I \times R \). This law assumes that the resistance of the device is constant, which isn't always the case in real-world scenarios. As such, some devices or components do not follow Ohm's Law. Two notable examples are:
1. **Diodes**: A diode is a semiconductor device that allows current to flow in one direction only. Its behavior is non-linear, meaning its resistance changes depending on the voltage applied across it. When a diode is forward-biased (voltage applied in the direction that allows current flow), it has a low resistance and allows current to pass through. However, when reverse-biased (voltage applied in the opposite direction), the resistance is extremely high, ideally approaching infinity, and it blocks current flow. This non-linear relationship between voltage and current means diodes do not obey Ohm's Law.
2. **Transistors**: Transistors are semiconductor devices used to amplify or switch electronic signals. They have three terminals: the emitter, base, and collector. The behavior of a transistor is complex and depends on the voltage and current applied to these terminals. In different operating regions (cutoff, active, and saturation), the relationship between the input and output currents and voltages is non-linear. For instance, in the active region of a bipolar junction transistor (BJT), the relationship between the base-emitter voltage and the collector current is exponential, not linear as Ohm's Law would suggest.
These devices are essential in modern electronics, but their behavior requires more sophisticated models and equations beyond Ohm's Law to describe accurately.
1. **Diodes**: A diode is a semiconductor device that allows current to flow in one direction only. Its behavior is non-linear, meaning its resistance changes depending on the voltage applied across it. When a diode is forward-biased (voltage applied in the direction that allows current flow), it has a low resistance and allows current to pass through. However, when reverse-biased (voltage applied in the opposite direction), the resistance is extremely high, ideally approaching infinity, and it blocks current flow. This non-linear relationship between voltage and current means diodes do not obey Ohm's Law.
2. **Transistors**: Transistors are semiconductor devices used to amplify or switch electronic signals. They have three terminals: the emitter, base, and collector. The behavior of a transistor is complex and depends on the voltage and current applied to these terminals. In different operating regions (cutoff, active, and saturation), the relationship between the input and output currents and voltages is non-linear. For instance, in the active region of a bipolar junction transistor (BJT), the relationship between the base-emitter voltage and the collector current is exponential, not linear as Ohm's Law would suggest.
These devices are essential in modern electronics, but their behavior requires more sophisticated models and equations beyond Ohm's Law to describe accurately.
Ohm's Law states that the current (I) through a conductor between two points is directly proportional to the voltage (V) across the two points, and inversely proportional to the resistance (R) of the conductor. Mathematically, it is expressed as:
\[ V = IR \]
However, not all devices follow Ohm's Law. Here are two common types of devices that do not obey Ohm's Law:
1. **Nonlinear Resistors**: These resistors, such as diodes and light-emitting diodes (LEDs), have a resistance that changes with the applied voltage. For example:
- **Diodes**: In a diode, the current does not increase linearly with the voltage. Instead, a small voltage must be applied before significant current starts to flow. Once the threshold voltage is reached, the current increases exponentially with voltage.
- **LEDs**: Similar to diodes, LEDs have a characteristic where their resistance changes with the applied voltage, leading to a nonlinear relationship between voltage and current.
2. **Superconductors**: At very low temperatures, superconductors exhibit zero electrical resistance. For superconductors:
- **Zero Resistance**: Ohm's Law is not applicable in the traditional sense because the resistance \( R \) becomes zero. This results in the equation \( V = IR \) implying \( V = 0 \) for any current \( I \), which doesn’t align with the usual behavior of resistive components.
In these cases, the relationship between voltage and current does not follow the simple linear model described by Ohm's Law.
\[ V = IR \]
However, not all devices follow Ohm's Law. Here are two common types of devices that do not obey Ohm's Law:
1. **Nonlinear Resistors**: These resistors, such as diodes and light-emitting diodes (LEDs), have a resistance that changes with the applied voltage. For example:
- **Diodes**: In a diode, the current does not increase linearly with the voltage. Instead, a small voltage must be applied before significant current starts to flow. Once the threshold voltage is reached, the current increases exponentially with voltage.
- **LEDs**: Similar to diodes, LEDs have a characteristic where their resistance changes with the applied voltage, leading to a nonlinear relationship between voltage and current.
2. **Superconductors**: At very low temperatures, superconductors exhibit zero electrical resistance. For superconductors:
- **Zero Resistance**: Ohm's Law is not applicable in the traditional sense because the resistance \( R \) becomes zero. This results in the equation \( V = IR \) implying \( V = 0 \) for any current \( I \), which doesn’t align with the usual behavior of resistive components.
In these cases, the relationship between voltage and current does not follow the simple linear model described by Ohm's Law.