P4 And P5 - Electricity And Circuits Flashcards

Question

What is a heater?

Answer 1

Designed to transfer the energy from an electric current to heat surroundings.

Answer 2

Emits light when a current passes through it.

Answer 3

The resistance of an appliance is R= V/I A filament lamp’s resistance increases as the filament’s temperature increases. Diode forward resistance is low. Diode reverse resistance is high. A thermistors resistance decreases if it’s temperature increases. An LDRs resistance decreases if the light intensity on it increases.

Answer 4

For components in series: The current is the same in each component The total potential difference is shared between the components Adding their resistances gives the total resistance For cells in series, acting in the same direction, the total potential difference is the sum of their individual potential differences. Total resistance - Rtotal = R1 + R2 Adding more resistors in series increases the total resistance because the current through the resistors is reduced and the total potential difference across them is unchanged.

Answer 5

For components in parallel: The total current is the sum of the currents through the separate components. The bigger the resistance of a component, the smaller the current that will pass through that component. The current through a resistor in a parallel circuit is: I = V / R Adding more resistors in a parallel circuit decreases the total resistance because the total current through the resistors is increased and the total potential difference across them in unchanged 1/Rt = 1/R1+ 1/R2 + 1/R3

Answer 6

Not an Ohmic resistor As the temp of the filament lamp increases, the resistance also increases. Filament bulbs get hot, and therefore waste energy- banned in UK to reduce emissions. Graph has a straight line which begins to slope as the extra resistance comes from heat.

Answer 7

Electrical appliances are connected to the mains supply by three core cables. They have 3 wires inside with a core of copper and a colours plastic coating. Always the same for every appliance - easy to tell apart Brown (BR) is live wire from the power station, provides alternating current. Blue (BL) neutral wire, taking energy back to the power station. Yellow/green stripes - Earth wire

Answer 8

Repeatedly reverses direction. Doubles the amount of potential difference, so more energy is transferred. Produced by alternating voltages in which the positive and negative ends keep alternating. UK mains supply uses this

Answer 9

Typical power station generates electricity at an alternating voltage of 25,000 volts. Step up transformers are uses at power stations to transfer electricity to the National Grid. These transformers are used to make the size of the alternating PD much bigger, typically from 25,000V to about 132000V Step down transformers are used to supply electricity from the national grid to consumers. Homes and offices in the UK are supplied with mains electricity that provides the same power as a 230V direct current supply. Factories use much more power than homes, so they are supplied with a p.d. of 100kV or 33kV

Answer 10

Electrons only moving in one direction. Batteries/cells can only supply direct current (d.c.) Created by a direct voltage, where P and N ends of the source are fixed.

Answer 11

Socket cases are made from stiff plastic materials that enclose the electrical connections. Plastic is used because it is a god electrical insulator. Mains cable made up of two/three copper wires surrounded by an outer layer of flexible plastic material. In a three pin plug the Earth wire is connected to the longest pin in a plug and is used to earth the metal case of a mains appliance.

Answer 12

• material (conductivity) • thickness of wire - thicker = less resistance • length • temperature - hotter = more resistance More current - more friction - temp increase - more resistance/loss of energy reduce current by increasing voltage, and still have the same power

Answer 13

• total resistance is less than the resistance of the smallest resistor

Answer 14

• total resistance is less than the resistance of the smallest resistor

Answer 15

• total resistance is less than the resistance of the smallest resistor