Module 4 - Chapter 9 - Energy, power and resistance Flashcards
What is potential difference?
The potential difference is a measure of the transfer of energy by charge carriers. It is also called voltage and is measured in volts (V).
What is 1 volt?
1 volt is the p.d. across a component when 1J of energy is transferred per unit charge passing through the component.
1V = 1J/C
What is the equation for p.d. / voltage?
V=W/Q
voltage (V) = energy transferred / charge (C)
V=IR
voltage (V) = current (A) x resistance (Ω)
What is a voltmeter?
A voltmeter is used to measure p.d., however, unlike ammeters, it is connected in parallel to a component rather than in series.
What is e.m.f.?
The electromotive force is used to describe when work is done on the charge carriers. As a charge goes through a component like a cell, battery or power pack, they gain energy, the greater the e.m.f., the more energy per coulomb is transferred to the charge in electrical energy. It is define as the energy transferred from chemical to electrical energy per unit charge.
What is the equation for e.m.f.?
ε = W/Q
e.m.f (V) = energy transferred / charge (C)
What is an electron gun?
An electron gun is a device used to produce a narrow beam of electrons.
How does an electron gun work?
In most cases a small filament is heated to give the electrons kinetic energy. Eventually, some of them gain enough kinetic energy to escape the surface of the metal, this is known as thermionic emission. The electrons then go through a vacuum with a high p.d. between the filament and an anode. Therefore, the electrons accelerate towards the anode. If the anode has a hole in it, then a thin stream of electrons in line with this hole will pass through, creating a beam of electrons with a specific kinetic energy.
What is the equation linking work done on the electron and kinetic energy gained?
eV = 1/2mv²
elementary charge x p.d. (V) = 1/2 x mass x velocity²
What happens if you increase the p.d. in the electron gun?
The greater the p.d., the greater the kinetic energy since more energy will be transferred to the electrons
What is resistance?
Resistance is a measure of the opposition to the flow of charge through a component. The higher the resistance, the more energy required for charge to flow.
What is the equation for resistance?
R = V/I
resistance (Ω) = p.d. (V) / current (A)
What is Ohm’s law?
Ohm’s law states that for a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the p.d. across its ends.
What would the I-V graph for a resistor look like?
The I-V graph of a resistor would have a constant gradient (straight line).
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What would the I-V graph for a filament lamp look like?
The I-V graph for a filament lamp has a changing gradient, it has an an almost S shape.
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