MASTERY MATERIALS ELEX 1 Flashcards
The unit of quantity of electricity is the:
coulomb
Electromotive force is provided by:
an electric current
The coulomb is a unit of
quantity of electricity
In order that work may be done:
a supply of energy is required
The ohm is the unit of:
resistance
The unit of current is the:
ampere
Which of the following formulae for electrical power is incorrect?
- V^2/R
- I^2R
- VI
- V/I
V/I
This is for RESISTANCE
Which of the following statements is true?
* An electrical insulator has a high resistance
* Electric current is measured in volts
* An ammeter has a low resistance and must be connected in parallel with a circuit
* 200kΩ resistance is equivalent to 2MΩ
An electrical insulator has a high resistance
Insulator - opposes flow of current
What must be known in order to calculate the energy used by an electrical appliance?
power and time of operation
Voltage drop is the:
difference in potential between two points
When an atom loses an electron, the atom:
becomes positively charged
The unit of resistivity is:
ohm metre
SI unit : ohm metre (Ω⋅m)
The symbol for the unit of temperature coefficient of resistance is:
Ω/Ω◦C
◦C^-1 or 1/◦C
A colour coding of red-violet-black on a resistor indicates a value of:
270Ω±20%
A resistor marked as 4K7G indicates a value of:
4.7 kΩ±2%
F, G, J, K, or M, which refers to a permissible tolerance of ±1%, ±2%,±5%, ±10%, and ±20% respectively.
A battery consists of:
a number of cells
Which of the following statements is false?
- A nickel cadmium cell is an example of a primary cell
- When a cell is being charged its terminal p.d. exceeds the cell e.m.f.
- A secondary cell may be recharged after use
- A Leclanché cell is suitable for use in torches
A nickel cadmium cell is an example of a primary cell
Examples of secondary batteries include nickel-cadmium (NiCd), lead acid, and lithium ion batteries.
Which of the following statements is false?
When two metal electrodes are used in a simple cell, the one that is higher in the electrochemical series:
- reacts most readily with oxygen
- acts as an anode
- is always the negative electrode
- tends to dissolve in the electrolyte
acts as an anode
Which of the following statements is true?
* The capacity of a cell is measured in volts
* A positive electrode is termed the cathode
* Galvanizing iron helps to prevent corrosion
* A primary cell converts electrical energy into chemical energy
Galvanizing iron helps to prevent corrosion
The greater the internal resistance of a cell:
- the less the e.m.f.
- the less the terminal p.d.
- the greater the e.m.f
- the greater the terminal p.d.
the less the terminal p.d.
The negative pole of a dry cell is made of:
zinc
The energy of a secondary cell is usually renewed:
- by heating it
- by passing a current through it
- it cannot be renewed at all
- by renewing its chemicals
by passing a current through it
Which of the following statements is true?
* A lithium battery is used in watches and is not rechargeable
* A zinc carbon battery is rechargeable and is not classified as hazardous
* An alkaline manganese battery is used in torches and is classified as hazardous
* A nickel cadmium battery is not rechargeable and is classified as hazardous
A lithium battery is used in watches and is not rechargeable
The effect of connecting an additional parallel load to an electrical supply source is to increase the:
- current taken from the source
- resistance of the load
- p.d. across the load
- voltage of the source
current taken from the source
The equivalent resistance when a resistor of 1/3Ω is connected in parallel with a 1/4Ω resistance is:
1/7Ω
A 10Ω resistor is connected in parallel with a 15Ω resistor and the combination in series with a 12Ω resistor. The equivalent resistance of the circuit is:
18Ω
When three 3Ω resistors are connected in parallel, the total resistance is:
1Ω
The total resistance of two resistors R1 and R2 when connected in parallel is given by:
- 1/R1 + 1/R2
- R1R2/(R1+ R2)
- R1+ R2
- (R1+ R2)/R1R2
Electrostatics is a branch of electricity concerned with
- energy flowing across a gap between conductors
- energy in the form of charges
- charges in motion
- charges at rest
charges at rest
The capacitance of a capacitor is the ratio
* p.d. between plates to plate spacing
* p.d. between plates to thickness of dielectric
* charge to p.d. between plates
* p.d. between plates to charge
charge to p.d. between plates
State which of the following is FALSE. The capacitance of a capacitor
- is proportional to the cross-sectional area of the plates
- is proportional to the relative permittivity of the dielectric
- depends on the number of plates
- is proportional to the distance between the plates
State which of the following is false. The capacitance of a capacitor
Which of the following statements is false?
- A paper capacitor generally has a shorter service life than most other types of capacitor
- An electrolytic capacitor must be used only on a.c. supplies
- An air capacitor is normally a variable type
- Plastic capacitors generally operate satisfactorily under conditions of high temperature
An air capacitor is normally a variable type
The capacitance of a variable air capacitor is at maximum when:
* the movable plates are closer to one side of the fixed plate than to the other
* both sets of plates are exactly meshed
* the movable plates are most widely separated from the fixed plates
* the movable plates half overlap the fixed plates
both sets of plates are exactly meshed
The unit of magnetic flux density is the:
* ampere per metre
* weber per metre
* weber
* tesla
- tesla - magnetic flux density or magnetic induction (B)
- ampere per metre - magnetic field strength
- weber per metre - not a standard unit
- weber - magnetic flux (Φ)
Which of the following statements is false?
- The remanence of a ferrous material is measured in ampere/metre
- Energy loss due to hysteresis is greater for harder magnetic materials than for softer magnetic materials
- Absolute permeability is measured in henrys per metre
- For non-magnetic materials reluctance is high
The remanence of a ferrous material is measured in ampere/metre
it is measured in tesla (T) or gauss (G)
The effect of an air gap in a magnetic circuit is to:
* reduce the magnetomotive force
* divide the flux
* increase the reluctance
* reduce the flux density
increase the reluctance
Two bar magnets are placed parallel to each other and about 2cm apart, such that the south pole of one magnet is adjacent to the north pole of the other. With this arrangement, the magnets will:
- lose their magnetism
- have no effect on each other
- repel each other
- attract each other
attract each other
Opposite poles attract each other, while like poles repel each other
If a conductor is horizontal, the current flowing from left to right and the direction of the surrounding magnetic field is from above to below, the force exerted on the conductor is:
* from below to above
* away from the viewer
* from left to right
* towards the viewer
away from the viewer
Applying Fleming’s Left-Hand Rule:
Middle Finger (Current, I): Pointing to the right (from left to right).
Index Finger (Magnetic Field, B): Pointing downward (from above to below).
Thumb (Force, F): The direction your thumb points will indicate the direction of the force.
An electric bell depends for its action on:
* reversal of current
* a permanent magnet
* an electromagnet
* a hammer and a gong
an electromagnet
There is a force of attraction between two current-carrying conductors when the current in them is:
* in opposite directions
* in the same direction
* of the same magnitude
* of different magnitude
in opposite directions
The magnetic field due to a current-carrying conductor takes the form of:
- rectangles
- straight lines radiating outwards
- concentric circles
- wavy lines
concentric circles
A bar magnet is moved at a steady speed of 1.0m/s towards a coil of wire which is connected to a centre-zero galvanometer. The magnet is now withdrawn along the same path at 0.5 m/s. The deflection of the galvanometer is in the
* same direction as previously, with the magnitude of the deflection halved
* opposite direction as previously, with the magnitude of the deflection halved
* opposite direction as previously, with the magnitude of the deflection doubled
* same direction as previously, with the magnitude of the deflection doubled
opposite direction as previously, with the magnitude of the deflection halved
Which of the following is false?
* The direction of an induced e.m.f. is always such as to oppose the effect producing it
* An induced e.m.f. is set up whenever the magnetic field linking that circuit changes
* The induced e.m.f. in any circuit is proportional to the rate of change of the magnetic flux linking the circuit
* Fleming’s left-hand rule or Lenz’s law may be used to determine the direction of an induced e.m.f.
Fleming’s left-hand rule or Lenz’s law may be used to determine the direction of an induced e.m.f.
Fleming’s Left-Hand Rule is used to determine the direction of force on a current-carrying conductor in a magnetic field
The effect of inductance occurs in an electrical circuit when:
- the flux is changing
- the current is changing
- the resistance is changing
- the voltage is changing
the current is changing
Inductors opposes the changes in current flow
Which of the following statements is false?
The inductance of an inductor increases:
- when wound on an iron core
- as the number of turns increases
- as the cross-sectional area of the coil decreases
- with a short, thick coil
as the cross-sectional area of the coil decreases
The inductance of an inductor increases as the cross-sectional area of the coil increases
102
A strong permanent magnet is plunged into a coil and left in the coil. What is the effect produced on the coil after a short time?
- The insulation of the coil burns out
- The coil winding becomes hot
- A high voltage is induced
- There is no effect
