Wiktor Wise
Electrical resistance is an important property of electricity that controls the flow of current in electrical systems. It is measured in ohms and can be used to identify installation errors, poor connections, and failed components. Materials with high resistance restrict the flow of electrons and require more voltage to function. This property of resistance is beneficial in everyday electrical devices such as toasters and incandescent light bulbs, which require heat to function. To control the amount of current flowing through these devices, they are designed with components that have high electrical resistance.
| Characteristics | Values |
|---|---|
| Purpose | To restrict the flow of electricity and protect the components in the circuit |
| Measurement | Can be measured using a multimeter or an ohmmeter |
| Unit | Ohm (Ω) |
| Relation to Voltage | Materials with high resistance require more voltage (EMF) to make the electricity flow |
| Relation to Heat | Resistance causes some of the electrical energy to turn into heat |
| Types of Resistors | Wire Wound, Carbon-Composition, Integrated |
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What You'll Learn
Toasters
The heating element in a toaster is typically made of a high-resistance wire, often a nickel-chromium alloy known as nichrome. Nichrome wire has high resistance to electricity, which means it opposes the flow of electric current. This resistance generates heat as the electrons encounter friction while passing through the wire. The high resistance of nichrome wire allows it to reach high temperatures without melting or burning, making it ideal for toasting bread.
The nichrome wire in a toaster is carefully mounted on insulators to ensure it follows the desired path. This mounting prevents the wire from creating a shorter path, which would reduce the circuit's resistance and impact the toasting process. The wire is also supported by non-conducting brackets, often made of ceramic, to further ensure the wire's path and maintain the necessary resistance for proper toasting.
To control the darkness of the toast, toasters use a variable resistor, which changes the rate at which the capacitor charges. This, in turn, controls the timer that releases the toast from the electromagnet. By adjusting the resistance, users can control how long the bread stays in the toaster, determining the level of browning. Some older or less sophisticated toasters use a bi-metallic strip that bends with heat to turn off the electromagnet, but this method is less consistent.
Overall, the toaster's ability to generate heat and brown bread relies on the high resistance of the nichrome wire, which converts electrical energy into heat energy. The careful management of resistance through the circuit board, mounting, and user controls ensures that the toaster functions safely and effectively.
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Light bulbs
In an electrical circuit, resistance is a crucial factor that controls the flow of current. It is measured in ohms, and a higher resistance results in a lower current flow. This relationship between voltage, current, and resistance can be described by Ohm's Law, which states that voltage (V) is equal to the product of current (I) and resistance (R). Therefore, in a light bulb, a higher resistance will lead to a lower current when the voltage is constant.
The brightness of a light bulb is influenced by its resistance and wattage. A higher resistance in the filament results in a brighter bulb as more energy is dissipated and converted into light. This is because a higher resistance causes a greater build-up of energy, which is then released as light and heat. Therefore, a 10-watt bulb will have a higher resistance than a 20-watt bulb, as the former will appear brighter due to its higher resistance.
However, it is important to note that the relationship between resistance and brightness is complex. Some sources suggest that a brighter bulb has a lower resistance than a dimmer bulb. This is because a lower resistance allows for a higher current, resulting in increased power and, consequently, a brighter light output. Additionally, in a parallel circuit, bulbs with lower resistance will shine brighter as they experience a higher current flow compared to bulbs in a series circuit.
Overall, light bulbs require high resistance to function, and this resistance plays a crucial role in determining the brightness and power consumption of the bulb. The specific relationship between resistance and brightness depends on various factors, including the type of bulb, the circuit configuration, and the interaction between current, voltage, and resistance.
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Resistors
A resistor is a passive electrical component that limits or creates resistance in the flow of electric current. Resistors are found in almost all electrical networks and electronic circuits. They are commercially available with resistance values over a range of more than nine orders of magnitude. The resistance is measured in ohms (Ω), the SI unit of electrical resistance, named after Georg Simon Ohm. One Ω represents the electrical resistance between two points when a voltage of one volt is applied across the points, resulting in a current of one ampere, or amp.
The choice of resistor technology is specific to its purpose. For example, the manufacturing technique of carbon composition creates a low-precision resistor but is still used for specific applications where high-energy pulses occur. Metal and metal oxide film are widely used today and have better properties for stability and tolerance. They are also less influenced by temperature variations. For the highest requirements on precision and stability, metal foil resistors are used.
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Multimeters
There are two main types of multimeters: analog and digital. A digital multimeter will automatically begin taking a resistance measurement as soon as it is turned on and will display OLΩ. The MΩ symbol may also appear on the display due to the high resistance of open (unattached) test leads. When the leads are connected to a component, the multimeter will automatically adjust to the best range. The range can also be manually set by pressing the Range button.
To measure resistance with a multimeter, the circuit's power must be turned off. The black test lead is plugged into the common input jack, and the red or yellow lead is plugged into the resistance input jack. The probe tips are then touched across the component or portion of the circuit for which the resistance is being measured. The reading can then be viewed, and the unit of measurement (ohms, kilohms, or megohms) should be noted. It is important to know what reading to expect before testing and to wear appropriate personal protective equipment (PPE) as circuits should be assumed to be live until proven otherwise.
There are several factors that can affect resistance readings, including temperature, foreign substances such as dirt or oil, and body contact with the metal ends of the test leads. It is important to avoid touching the metal parts of the test leads to avoid errors. To capture a stable measurement, the HOLD button on the multimeter can be pressed. The MIN/MAX button will capture the lowest and highest measurements, and the multimeter will beep each time a new reading is recorded.
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Ohmmeter
An ohmmeter is a tool for measuring electrical resistance, which is the opposition offered by a circuit or component to the flow of electric current. It is an essential device for identifying electrical issues and ensuring the proper functioning of electrical systems.
The first ohmmeters were based on a meter movement known as a "ratiometer," which indicated resistance through the ratio of currents in two coils. Subsequent designs incorporated a small battery to apply voltage to a resistance via a galvanometer, forming a circuit by themselves. More advanced ohmmeters have electronic circuits that pass a constant current through the resistance and measure voltage, providing more precise readings.
Precision ohmmeters feature four terminals, known as Kelvin contacts. Two terminals manage the current flow, while the other two measure the voltage across the resistor. This setup, known as Kelvin sensing, ignores any voltage drop due to lead and contact resistances, ensuring accurate measurements, especially for very low resistances.
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Frequently asked questions
Devices such as toasters and incandescent light bulbs must have high resistance. This resistance causes the current to struggle to flow, generating heat and light.
An example of a device with a fixed-resistance value is a resistor. Resistors are components added to a circuit to restrict the flow of electricity and protect other components.
Electrical resistance is measured in ohms (Ω) and can be measured using a multimeter or an ohmmeter. A multimeter can measure voltage, current, resistance, and other electrical parameters, while an ohmmeter only measures resistance.
