Topic 5 Flashcards
Define electric potential
the potential energy that each coulomb of positive charge would have if placed at that point in the field
Define electric potential difference
The work done per unit charge moving a positive test charge between two points in a circuit. measured in volts.
Define potential difference
the potential difference or p.d. is the energy transferred when one coulomb of charge passes from one point to the other point
Where does the potential difference act?
A potential difference acts across a component
What is the energy transfer equal to?
Energy transferred is equal to the amount of electric potential energy gained or to the amount of kinetic energy gained
Define the electonvolt
Unit of energy. The energy required to move one electron through a PD of one volt. W (eV) = q (electron charges) x V (volts)
1 eV = 1.6 x 10-19 J
Define electric current
The rate of flow of charge. Unit is the ampere. Conventional current flows from positive to negative
What is current?
The current is defined in terms of the force per unit length between parallel current-carrying conductors
Define resistance
The ratio of potential difference across a conductor to current through the conductor
State Ohm’s Law
The current through a conductor is directly proportional to the voltage across its ends if the temperature and other conditions are constant
What is the difference between ohmic and non-ohmic behavior?
In ohmic behavior, the voltage is directly proportional to the current. While in the non-ohmic behavior voltage is not proportional to current.
Define power
The rate of converting energy. Unit is watt (W) = 1J/S
Define electromotive force
The total electrical energy given by the battery to each coulomb of charge OR the terminal potential difference of the source when no current flows
Define internal resistance
The resistance of the battery. Some of the energy provided by the source is converted to heat here and is not available in the external circuit components.
Define terminal potential difference
The potential difference measured across the terminals of the source which is less than the emf due to the internal resistance of the source.
How are resistors in a parallel circuit connected?
similar to a ladder
What is the potential difference across each resistor in parallel circuits?
The potential difference across each resistor in parallel is the same
What is the current in a parallel circuit?
The current in the main circuit is the sum of the currents in each of the parallel branches
How are the resistors connected in a series circuit?
similar to a chain
What is the current through each resistor in a series circuit?
The current through each resistor in the series is the same
What is the total potential difference across the resistors in a series circuit?
The total potential difference, V, across the resistors is the sum of the potential differences across the separate resistors
What is the combined resistance in a series circuit?
The combined resistance R in the circuit is the sum of the separate resistors
What is an ammeter and where does it connect?
Instrument which measures current in a circuit. It must be connected in series with the current it measures and has a very low resistance.
What is a voltmeter and where does it connect?
Instrument which measures potential difference in a circuit. It must be connected in parallel with the potential difference it measures and has a very high resistance.
What is the ideal resistance of an ideal ammeter?
zero resistance
What is the ideal resistance of an ideal voltmeter?
infinite resistance
Define potential divider
The potential divider of a source is divided over two resistors in series in proportion to their resistances
Define electrical sensors
A component whose electrical properties (usually resistance) changes with its physical conditions.
Define thermistor
A resistor whose resistance falls when its temperature rises.
Define light dependent resistor
A resistor whose resistance falls as the intensity of light falling on it increases.
Define strain gauge
A long thin wire whose resistance increases when it is stretched
Define sensor circuits
One of the resistors in a potential divider is replaced by a sensor so that the potential divider across the resistors in the potential divider changes as a physical condition changes (eg temperature, light intensity or strain)
Two resistors of equal resistance are connected in series to a battery with negligible internal resistance. The current drawn from the battery is 1.0 A. When the two resistors are connected in parallel to the battery the current drawn will be
A. 0.5 A.
B. 1.0 A.
C. 2.0 A.
D. 4.0 A.
D. 4.0 A.
In the diagram the voltmeter V has a resistance of 100 kΩ and is connected such as to measure the potential difference across the 100 kΩ resistor. The battery has an emf of 5.0 V and negligible internal resistance.
The reading on the voltmeter will be
A. 4.0 V.
B. 2.5 V.
C. 1.0 V.
D. zero.
C. 1.0 V
A cell has an emf E and an internal resistance r. An external resistor which also has resistance r is connected across the terminal of the cell. The power dissipated in the external resistor is
A. E2/r
B. E2/2r
C. E2/4r
D. zero.
C. E2/4r
An electric immersion heater has a power rating of 3 kW and is designed to operate from a 250 V supply. For safety reasons the value of the fuse that should be used is
A. 3 A.
B. 5 A.
C. 10 A.
D. 13 A.
D. 13 A.
The primary of an ideal transformer has 1000 turns and the secondary 100 turns. The current in the primary is 2 A and the input power to the primary is 12 W. Which one of the following about the secondary current and the secondary power output is true?
secondary current secondary power output
A. 20 A 1.2 W
B. 0.2 A 12 W
C. 0.2 A 120 W
D. 20 A 12 W
D. the secondary current is 20 A and the secondary power output is 12 W
In a laboratory experiment, a variable voltage power supply is used to provide voltage versus current data for two unequal resistors. These two resistors are first connected separately to the power supply, then as a series combination and then as a parallel combination. The four sets of results are plotted as shown.
Which set of results would correspond to the two resistors connected in parallel?
A. 1
B. 2
C. 3
D. 4
A. 1
A potential difference is applied across a pair of parallel plates in a vacuum. A proton between the plates experiences an acceleration of magnitude a. What would be the acceleration of an alpha particle?
A. a/4
B. a/2
C. a
D. 2a
B. a/2
Two resistors in parallel form R1 and R2 part of a circuit. has R1 three times the resistance of , and R2 the total current flowing into the parallel pair is 12 A as shown.
A. 3 A.
A simple form of lighting for decorating trees sometimes consists of a string of small light bulbs connected in series as shown.
With this simple system, if one of the bulbs burns out (its filament breaks) then the others will
A. all go out.
B. glow dimmer than before.
C. glow just as bright as before.
D. glow brighter than before.
A. all go out.
To start a car with a flat battery, the battery can be connected to the battery in another car using two cables. These are called “jumper cables” or “jump leads” and have low resistance. Suppose a good quality jumper cable has resistance R. A cheaper cable of the same length but half the cable diameter would have resistance
A. R/4
B. R/2
C. 2R.
D. 4R.
D. 4R.
A student constructs a ìvoltage dividerî which will provide an output voltage of 6 V from an input voltage of 9 V. She connects two resistors and as shown.
The ratio of the resistances R1: R2 must be
A. 1 : 2 .
B. 2 : 1 .
C. 2 : 3 .
D. 3 : 2 .
A. 1 : 2
The graph below shows the current/voltage characteristics of a filament lamp.
The resistance of the filament at 4.0 V is
A. 250 ohms.
B. 4000 ohms.
C. 8000 ohms.
D. 64000 ohms.
A. 250 ohms.
An electric motor is used to raise a weight of 2.0 N. When connected to a 4.0 V supply, the current in the motor is 1.5 A. Assuming no energy losses, the best estimate for the maximum steady speed at which the weight can be raised is
A. 0.3ms-1
B. 3.0 ms-1
C. 9.0 ms-1
D. 12.0 ms-1
B. 3.0 ms-1
The variation with potential difference V of the current I in an electric lamp is shown below
At point P, the current is Ip, the potential difference is Vpand the gradient of the tangent to the curve is G. What is the resistance of the lamp at point P?
A. 1/G
B. G
C. Ip/Vp
D. Vp/Ip
D. Vp/Ip
A cell of e.m.f. E and internal resistance r is connected to a variable resistor. A voltmeter is connected so as to measure the potential difference across the terminals of the cell. Which one of the following is the correct circuit diagram of the arrangement?
B
The ampere is defined in terms of
A. the force between a magnet and a coil carrying a current.
B. the force between two long current carrying wires.
C. the amount of charge that passes any cross-sectional area of a wire in unit time.
D. the number of electrons that pass any cross-sectional area of a wire in unit time
B. the force between two long current carrying wires.
Which one of the following shows a correct circuit, using ideal voltmeters and ammeters, for measuring the I-V characteristic of a filament lamp?
B
Which one of the following is a fundamental unit?
A. Coulomb
B. Ohm
C. Volt
D. Ampere
D. Ampere
A battery is connected in series with a resistor R. The battery transfers 2000 C of charge completely round the circuit. During this process, 2500 J of energy is dissipated in the resistor R and 1500 J is expended in the battery. The e.m.f. of the battery is
A. 2.00 V.
B. 1.25 V.
C. 0.75 V.
D. 0.50 V.
A. 2.00 V.
In the circuit below, which meter is not correctly connected?
A. 1
B. 2
C. 3
D. 4
D. 4
The electron volt is defined as
A. a unit of energy exactly equal to 1.6x10-19 J.
B. a fraction 1/13.6 of the ionization energy of atomic hydrogen.
C. the energy gained by an electron when it moves through a potential difference of 1.0 V.
D. the energy transfer when 1.0 C of charge moves through a potential difference of 1.0 V
C. the energy gained by an electron when it moves through a potential difference of 1.0 V.
In the circuit below, n charge carriers pass the point P in a time t. Each charge carrier has charge q.
A. q/t
B. nq/t
C. qt/n
D. nqt
B. nq/t
The current in the circuit shown below is constant when the switch is closed
The energy transfer in the internal resistance r of the battery is 15 J when a charge of 40 C passes through it. For the same amount of charge, 45 J of energy is transferred in the resistor R. Which of the following gives the e.m.f. of the battery?
A. 15/40 V
B. 30/40 V
C. 45/40 V
D. 60/40 V
D. 60/40 V
The graph shows the variation with applied potential difference V of the current I in an electrical component.
Which one of the following gives the resistance of the component at point P?
A. The gradient of the line at P
B. The reciprocal of the gradient of the line at P
C. The ratio I1/V1
D. The ratio V1/I1
D. The ratio V1/I1
The diagrams below show combinations X, Y and Z of three resistors, each resistor having the same resistance.
Which one of the following shows the resistances of the combinations in increasing order of magnitude?
D
A battery of e.m.f. E and negligible internal resistance is connected to three resistors, each of resistance R, a voltmeter and a switch, as shown below.
The voltmeter has infinite resistance.
What are the readings on the voltmeter when the switch is open and when it is closed?
C
The graph below shows the variation with voltage V of the current I in three resistors X, Y and Z
Which of the following corresponds to resistors for which the resistance increases with increasing current?
A. X only
B. Z only
C. X and Z
D. Y and Z
A. X Only
The element of an electric heater has a resistance R when in operation. What is the resistance of a second heater that has a power output three times as large at the same operating voltage?
A. R/9
B. R/3
C. 3R
D. 9R
B. R/3
In the two circuits X and Y below, each cell has an e.m.f. E and negligible internal resistance. Each resistor has a resistance R.
The power dissipated in circuit X is P. The best estimate for the power dissipated in circuit Y is
A. P/4 .
B. P/2 .
C. 2P.
D. 4P.
C. 2P
A proton of mass m and charge e is accelerated from rest through a potential difference V. The final speed of the proton is
A. (2Ve/m)1/2
B. 2Ve/m
C. (Ve/m)1/2
D. Ve/m
A. (2Ve/m)1/2
A battery is connected to a resistor as shown below
The battery transfers energy EB when charge Q passes completely around the circuit and the resistor transfers energy ER. The e.m.f. of the battery is equal to
A. ER/Q
B. EB/Q
C. (EB + ER)/Q
D. (EB + ER)/Q
B. EB/Q
In the circuit shown below, the cell has negligible internal resistance.
Which of the following equations is correct?
A. I1=2I2
B. I1=2I3
C. I2=2I3
D. I3=2I1
C. I2=2I3
The graph below shows the variation with potential difference V of the current I in an electrical component.
Which one of the following is a correct statement about the resistance of the component?
A. For potential differences greater than V0, the resistance is constant.
B. For potential differences greater than V0, the resistance decreases with increasing potential difference.
C. The variation of current with potential difference is linear and so Ohm’s law is obeyed.
D. For potential differences less than V0, the resistance is zero.
B. For potential differences greater than V0, the resistance decreases with increasing potential difference.
In which one of the circuits is it possible to vary the current in the lamp by adjusting the variable resistor? The cell has negligible internal resistance.
A
Which of the following is a correct statement of Ohm’s law?
A. The resistance of a conductor is always constant.
B. The current in a conductor is always proportional to the potential difference across the conductor.
C. The resistance of a conductor increases with increasing temperature.
D. The resistance of a conductor is constant only if the temperature of the conductor is constant.
D. The resistance of a conductor is constant only if the temperature of the conductor is constant.
An electron and a proton are accelerated from rest through potential differences of the same magnitude. After acceleration the speed of the electron is ve and the speed of the proton is vp . Which of the following is the best estimate for the ratio vp/ve ?
A. 2000
B. (2000)1/2
C. 1/(2000)1/2
D. 1/2000
C. 1/(2000)1/2
A resistor of resistance 1.0 ohms is connected in series with a battery. The current in the circuit is 2.0 A. The resistor is now replaced by a resistor of resistance of 4.0 ohms. The current in this circuit is 1.0 A.
The best estimate for the internal resistance of the battery is
A. 1.0 ohms.
B. 2.0 ohms.
C. 4.0 ohms.
D. 5.0 ohms.
B. 2.0 ohms.
Which of the following is the correct value of the electronvolt, measured in SI Units?
A. 1.6 x 10–19N
B. 1.6 x 10–19 J
C. 9.1 x 10–31N
D. 9.1 x 10–31 J
B. 1.6 x 10–19 J
The graphs below are the current-voltage (I-V) characteristics of three electrical components P, Q and R.
Which component(s) has (have) constant resistance?
A. P only
B. R only
C. P and Q only
D. P and R only
A. P only
In the circuit below, resistors X, Y and Z are connected in series with a 9.0 V supply.
Resistors X and Z are fixed resistors of resistance 3000 ohms. The resistance of resistor Y may be varied between zero and 3000 ohms. Which of the following gives the maximum range of potential difference V across the resistors X and Y?
A. 0 to 6.0V
B. 3.0V to 6.0V
C. 4.5V to 6.0V
D. 4.5V to 9.0V
C. 4.5V to 6.0V
