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Question-51. Why does resistance of an LDR decrease when the light intensity increases?
Answer-51: Light energy helps the particles to line up and allow charges through more easily.
Question-52. When would an LDR be useful?
Answer-52: Light sensors - to switch on lights when it gets dark.
Question-53. To measure the resistance of a component, what measurements should be made?
Answer-53: Measurements of the current through the component and the potential difference across it.
Question-54. In the required practical on investigating I-V characteristics of components, what is the independen
Answer-54: The current through the component
Question-55. What happens to the potential difference across a wire when the length of the wire increases?
Answer-55: The longer the wire, the higher the resistance
Question-56. In a series circuit, what can be said about the current?
Answer-56: The current is the same through each component.
Question-57. In a series circuit, what can be said about the potential difference?
Answer-57: The sum of the potential difference across each component is equal to the potential difference of the battery
Question-58. In a series circuit, what can be said about the resistance?
Answer-58: The total resistance is the sum of the individual resistances.
Question-59. What is the equation for the total resistance of a series circuit?
Answer-59: Rtotal = R1 + R2 ...
Question-60. In the branches of a parallel circuit, what can be said about the current?
Answer-60: The total current is equal to the sum of the current in each branch
Question-61. In the branches of a parallel circuit, what can be said about the potential difference?
Answer-61: The potential difference across each branch is the same and the battery
Question-62. In the branches of a parallel circuit, what can be said about the resistance?
Answer-62: The total resistance in the circuit is less than the resistance of the lowest of the resistor in any branch
Question-63. Why does adding resistors in parallel decrease the total resistance?
Answer-63: There are more routes for electrons to take between the branches, so it is easier for current to flow.
Question-64. What does DC stand for?
Answer-64: Direct Current
Question-65. In what direction does DC current flow?
Answer-65: Current flows in one direction (positive to negative for conventional current)
Question-66. What type of circuits use DC?
Answer-66: Circuits powered by a cell or battery
Question-67. What does AC stand for?
Answer-67: Alternating Current
Question-68. What type of current does mains electricity use?
Answer-68: Alternating current
Question-69. What the frequency of the AC domestic electricity supply in the UK?
Answer-69: 50 Hz, (50 cycles per second)
Question-70. What is the potential difference of the domestic electricity supply in the UK?
Answer-70: 230 V
Question-71. How many wires make up the cables of most electrical appliances?
Question-72. Why is each wire wrapped in a plastic coating?
Answer-72: As a safety feature. The plastic acts as an insulator from the electricity
Question-73. What does the colour coding on each wire identify it as?
Answer-73: Brown - live wire
Blue - neutral wire
Green and yellow stripes - earth wire
Question-74. What does the live wire do, and what is its potential?
Answer-74: It carries the alternating potential from the power supply. The potential difference between the live wire and earth is around 230 V.
Question-75. What does the neutral wire do, and what is its potential?
Answer-75: It completes the circuit, and is close to earth potential (0 V).
Question-76. What does the earth wire do, and what is its potential?
Answer-76: It is a safety wire to stop the casing of the appliance from becoming live, so is at 0V and only carries a current if there is a fault.
Question-77. When is a live wire dangerous?
Answer-77: They are always dangerous when a current is flowing, because they carry a potential of 230V.
Question-78. Why is it dangerous to touch a live wire?
Answer-78: A persons potential is 0V. Touching the live wire causes a potential difference of 230V and the charge is carried through the person.
Question-79. What is power?
Answer-79: The amount of energy transferred per second
Question-80. What is the unit of power and the unit symbol?
Answer-80: Watts, W
Question-81. What does the amount of energy an appliance transfers depend on?
Answer-81: The power of the appliance and how long it is switched on for.
Question-82. What does work have to do with electric circuits?
Answer-82: Work is done when charge flows in a circuit.
Question-83. What two word equations relate energy transferred, power, time, charge and potential difference?
Answer-83: Energy transferred = Power x Time energy transferred = Charge x Potential difference
Question-84. What two symbol equations relate energy transferred, power, time, charge and potential difference?
Answer-84: E = P t
E = Q V
Question-85. What is the unit and unit symbol of energy?
Answer-85: Joules, J
Question-86. What is the power transfer in a circuit related to?
Answer-86: The potential difference across the circuit, the current through it and the energy changes over time.
Question-87. What two word equations relate power, potential difference, current and resistance?
Answer-87: Power = potential difference x current; Power = (current)2 x resistance
Question-88. What two symbol equations relate power, potential difference, current and resistance?
Answer-88: P = V I or P = I2 R
Question-89. What does the power rating of an appliance mean?
Answer-89: The maximum operating power that is safe for the appliance.
Question-90. What is the National Grid?
Answer-90: The National Grid is a system of cables and transformers linking power stations to consumers.
Question-91. What is a transformer?
Answer-91: A device which alters the potential difference and current of electricity in the cables.
Question-92. What does a step-up transformer do?
Answer-92: They are used to increase the potential difference from the power station to the transmission cables
Question-93. Why do we increase the potential difference across the cables?
Answer-93: To decrease current and reduce the energy loss due to heating.
Question-94. What does a step-down transformer do?
Answer-94: They are used to decrease the potential difference for safe domestic use.
Question-95. Why is static-electricity called "static"?
Answer-95: It is related to "static" (or still) electrons which build up on materials.
Question-96. What type of charge do electrons have?
Answer-96: Negative charge
Question-97. How is static electricity produced?
Answer-97: When certain insulating materials are rubbed, the friction causes negatively charged electrons to move from one material to another
Question-98. Which sub-atomic particle is transferred between materials to generate a static charge?
Answer-98: Negatively charged electrons
Question-99. If a material gains electrons what charge will it have?
Answer-99: The material that gains electrons becomes negatively charged.
Question-100. If a material loses electrons what charge will it have?
Answer-100: The material that loses electrons is left with an equal positive charge.
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