Edexcel Physics Unit 2 Classified past papers

 Classified past paper of Unit 2: Electricity 

EDEXCEL IGCSE past papers for code 4PH1/4PH0.

The paper has question from paper 1 and 2 from higher tier.

UNIT 2: Electricity classified past papers link for download is given below:

Download past paper here.

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Notes excerpt:

Calculating the resistance:

Ammeters: are connected in series to the resistor. It measures the amount of current flowing. Measured in Amperes or milliamperes (1 mA is 0.001 A)

Voltmeter: are connected in parallel with the resistor. Measured in Volts (V).

Resistance: Measured in ohms (ohm (Ω)). 1 kΩ is 1000 Ω.

Calculated using the equation:

V=IR

Ohm’s law:

States that when temperature is kept constant and current is proportional to the voltage. The resistor in such a case is said to be ohmic resistors. The voltage against current graph shows a linear graph (straight line passing through the origin-as shown in graph 1)

Resistance can be calculated using the formula: R=V*I.

When the resistor does not behave the same i.e., voltage is not proportional to the current, then it is said to be non-ohmic. In this case the voltage against current graph is a curve (as shown in graph 2). In non-ohmic resistors, when the current increases, resistance also increases and so the temperature increases.

 

The diode:

A device that regulates the flow of current in one direction and that is a forward voltage. When voltage is reversed there is no current flowing through the circuit.

LED: Light-Emitting Diode: A device that lights up when there is current through it. When there are is dim light, there is less resistance and when light intensity increases the resistance also increases.

 

Thermistor: A diode which reacts to surroundings temperature, the thermistors resistance decreases when temperature increases.     

Adding resistance:

When resistors are connected in series, the total resistance is calculated by adding up the resistance of each resistor.

Current, charge and voltage:

Current: measure of rate at which the electrical charge flows.

The flow is from the positive terminal of the battery to the negative terminal.

Charge: the amount of charge flowing in a circuit is measured in Coulombs (C).

Charge and Current are linked with equation shown below:

Q=I*T

Where Q=charge,

I=current,

T= time.

Equation relating voltage, charge and energy shown below: 

E=Q*V

E=Energy, Joules, J.

Q=Charge, Coulombs, C

V=Voltage, Volts, V

Current and voltage rules:

When appliances are connected in a series connection the amount of current flowing through each one of the appliances is equal.

If the appliances are connected in parallel, then the current is split either equally or unequally between them. But the input current is always equal to output current, so missing currents could be found using simple maths as shown in example below:

Rules of Current:

Current is same at any given point of series circuit.

The current splits up in parallel connection

Rules of Voltage:

In parallel: voltage across all appliances remain same. Whereas in series the voltage adds up to battery voltage.

Uses of parallel circuits:

·        Domestic appliances are connected in parallel so that all appliances receive full mains voltage and are individually operated with switch.

·        Voltmeters are always placed in parallel to measure voltage across them.

Uses of series circuits:

·        Lights of decoration are used in series connection as they require low voltages.

·        A switch is placed in series connection

·        An ammeter is connected in series

·        A resistor is connected in series with a component such as diode or thermistor to prevent overheating.

·        A fuse is connected in series and before the appliance as a safety measure.

Batteries: consists of two or more cells.

Cell; an individual cell.

Batteries connected in series as shown in circuit add up to produce a larger voltage. If they face in opposite direction then the resultant voltage is zero.

Electrostatics:

Rubbing a balloon and stick, causes the stick to become charged (as a result of friction) and when bought near to the hair it causes hair to rise. There is a positive charge on the ruler and a negative charge on the balloon. Like charges are repelled and opposite charge attract each other.

These charges come from the atom of substances. The atom has nucleus which has protons (positively charged particles) and neutrons (no charge) and outside the nucleus, there are electronic shells which have electrons (negative charged particles) orbiting around the nucleus.

There are equal number of positively charged particles (protons) and negatively charged particles (electrons) so the atom is neutral.

The gold leaf electroscope:

The metal rod and cap are insulated from the metal box and up to a thin gold leaf is attached to the end of metal rod. When the cap is negatively charged, the electrons flow in the metal and spread out through the metal box including gold leaf. So, the leaf moves away from the rod, as the like charges are repelled away from each other.

PRACTICAL:

Investigate how insulating material can be charged through friction (rubbing).

a.   Charge electroscope using high voltage. Note whether the electrode is positive or negatively charged.

b.   Rub the insulator with duster and hold insulator close to the electroscope.

c.   Movement of electroscope leaf helps deduce the following:

·        Is insulator charged.

·        Sign of the charge.

d.   Record the duster, insulator and sign of charge on duster and insulator.

e.   Repeat the process with other insulating materials.

Conductors:

Metas are good conductors of electricity, because they have free electrons which move about freely from positive to the negative terminal.

When an atom gains an electron, it becomes a negatively charged ion

When an atom loses an electron, it becomes positively charged ion.

 

Electrostatics at work:

A lightening occurs when the charged bas of clouds finds a conducting pathway in the air towards the ground or a tall object

Sparks: can cause an explosion in oil fumes. To prevent this type of explosion, the oil surfaces are covered with nitrogen. This gas does not burn, so explosion charges are reduced.

 

Electrostatic precipitation:

The burning of fossil fuel produces a lot of soot and this soot is removed before air escapes into the atmosphere by electrostatic precipitation.

The precipitator carries large negative charge and so when the soot passes through these, it becomes negatively charged and it is repelled away from the negative wires and attracted to positive plates and the soot sticks to positive plates and is removed later.

 

Photocopying:

The photocopy machine consists of light sensitive plate. When this plate is in dark surface, it is positively charged and when the plate is in light it is uncharged. The document to be copied is projected on to the plate and the dark portion of the plate becomes charged and a piece of paper is pressed on plate. The paper is positively charged. When the toner is heated, the paper is printed.

 

Electrostatic paint spraying:

Used to paint an even layer of paint on items such as car and bicycles. The nozzle of spray is negatively charged and when paint droplets leave the nozzle they also become negatively charged and like charges repel each other and make a fine mist. Compared to the paint droplets, the car is positively charged (relatively) and so the paint droplets get attracted to the car surface.