# Shared Flashcard Set

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16
Physics
08/26/2006

Term
 State Kirchhoff’s First Law
Definition
 The algebraic sum of the currents at the junction of a circuit is zero. (sum of currents into the junction = sum of currents out of junction)
Term
 State Kirchhoff’s Second Law
Definition
 The algebraic sum of the potential differences in a circuit is equal to the algebraic sum of the product of the resistance and current for each component
Term
 What is EMF?
Definition
 The electromotive force of a source of electrical energy is the energy converted into electrical energy (e.g. from chemical in a cell) when unit charge (in other words 1 coulomb) passes through it – total electrical energy per coulomb produced by a power supply when a current flows through it. This is found practically by connecting a voltmeter across the terminals in open circuit (i.e. when no other component is drawing current).
Term
 What is terminal voltage?
Definition
 Terminal voltage is the external potential difference of a circuit. It is the electrical energy per coulomb transferred into other forms (usually heat) when a current passes through the components. This is found practically by connecting a voltmeter across the terminals of the power supply when it is powering a circuit.
Term
 What is internal resistance? symbol ‘r’
Definition
 The internal resistance of a cell is the resistance offered by the chemicals in the cell itself. As a current passes through it some of the energy from the cell is converted to heat because of the internal resistance. Also some of the EMF of the cell is used to drive the current through the cell itself. This voltage is sometimes termed ‘lost volts’. It is the difference between the EMF and terminal voltage.
Term
 What is resistance?
Definition
 The resistance of a component is the ratio of the potential difference across its ends and the current passing through it. It is measured in ohms (symbol a capital omega). R = V/I
Term
 What is the equation for resistivity?
Definition
 'ro' = AR/l where:r = resistivity (ohm m) A = cross sectional area (m2) R = resistance (okm) l = length (m)
Term
 Give the equation for density (careful with the symbols!)
Definition
 'ro' = m/V
Term
 Give two equations for power. Then using V=IR get some useful derivations from them!
Definition
 P = IV E = Pt P = I (IR) = I2R P = V/R x V = V2/R E = (IV)t
Term
 What is the equation that defines current?
Definition
 I = delta Q/ delta tCurrent is the rate at which charge flows.
Term
 Quote the equation that defines voltage and use it to define EMF and potential difference of a circuit.
Definition
 V = W/Q where: W = energy transferred Q = charge V = voltage (Think of the equation as W = QV – for an electron volt of energy Q becomes ‘e’ the charge on an electron. So for W to be a full joule Q is 1 coulomb… you can then rearrange it…) The electromotive force of a source of electrical energy is the energy converted into electrical energy (e.g. from chemical in a cell) when unit charge (in other words 1 coulomb) passes through it – total electrical energy per coulomb produced by a power supply when a current flows through it. This is found practically by connecting a voltmeter across the terminals in open circuit (i.e. when no other component is drawing current). The external potential difference of a circuit is the electrical energy per coulomb transferred into other forms (usually heat) when a current passes through the components. This is found practically by connecting a voltmeter across the terminals of the power supply when it is powering a circuit.
Term
 State Ohm’s Law
Definition
 Ohm’s Law states that the current flowing through an ohmic conductor(e.g. a wire) is proportional to the potential difference across its ends, providing the temperature remains constant
Term
 State Hooke’s Law
Definition
 The extension produced in a wire or spring is directly proportional to the applied force providing the limit of proportionality has not been exceeded. This limit is usually reached at about the same time as the elastic limit.
Term
 Define tensile stress
Definition
 Tensile stress is the ratio of the stretching force to the cross sectional area of a wire that is being stretched. stress = F/A - unit = N/m2
Term
 Define tensile strain
Definition
 Tensile strain is the ratio of the extension (change in length) produced when a wire is stretched to the original length of the wire when no stretching force has been applied to it – strain = delta l/l (no unit)
Term
 Define the Young Modulus
Definition
 The Young Modulus is the ratio of the tensile stress to the tensile strain. E = (F/A)/( delta l/l) = (Fl)/(A delta l) - unit = N/m2
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