Physics P6 Ocr Gateway Circuits And Resistors

Front 1

What is current in the circuit?

Back 1

Current is the flow of charge (electrons) round the circuit and is measured in amps, A.

Front 2

When will current only flow?

Back 2

Current will only flow through a component if there is a voltage across the component.

Front 3

What is voltage in a circuit?

Back 3

Voltage is the driving force that pushes the current round. Voltage is measured in volts, V.

Front 4

What is resistance in a circuit?

Back 4

Resistance is anything in the circuit that reduces the current. Resistance is measured in ohms.

Front 5

What is resistance caused by?

Back 5

Resistance is caused by collisions in a conductor

Front 6

How is resistance increased by collisions? Explain?

Back 6

In a metal conductor, the electric charge is carried by electrons. When electrons flow through a conductor they collide with atoms in the metal - this causes resistance to occur. Collisions between electrons and atoms cause the atoms to vibrate. The more atoms vibrate, the more they get in the way of the electrons, so the more collisions there are. The increased the vibration of the atoms also increases the temperature in the conductor.

Front 7

What is a variable resistor?

Back 7

A variable resistor or rheostat is a resistor whose resistance can be changed. They are also used to vary the current flow in many different circumstances such as:

1. Increasing brightness

2. Increasing volume

Front 8

Why do longer wires have more resistance?

Back 8

Longer wires have more resistance, so less current flowing through them. This is because the longer the wire, the more atoms the electrons will collide with, increasing the resistance.

Front 9

What are variable resistors used for ?

Back 9

They are used for controlling the speed of motors and the brightness of bulbs. Turning the resistance down increases the speed of the motor o the brightness of a bulb.

Front 10

What are the factors affecting a wire's resistance?

Back 10

1. type of wire

2. length of wire

3. cross sectional area of the wire

4. temperature of the wire

Front 11

What is a potentiometer?

Back 11

1. an instrument for measuring an electromotive force by balancing it against the potential difference produced by passing a known current through a known variable resistance.

A potentiometer allows the current flowing in a circuit to be varied. This is achieved by altering the length of a wire included in the circuit. As the length of wire is increased the resistance increases, and so the current flowing in a circuit decreases.

A potentiometer, informally a pot, is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.

Front 12

Circuit symbols-

What is a cell symbol ?

Back 12

Front 13

Circuit symbols- What is a battery symbol ?

Back 13

Front 14

Circuit symbols- What is a power supply symbol ?

Back 14

Front 15

Circuit symbols- What is a switch open symbol ?

Back 15

Front 16

Circuit symbols- What is a switch closed symbol ?

Back 16

Front 17

Circuit symbols- What is a bulb symbol ?

Back 17

Front 18

Circuit symbols- What is a fixed resistor symbol ?

Back 18

Front 19

Circuit symbols- What is a variable resistor symbol ?

Back 19

Front 20

Circuit symbols- What is a ammeter symbol ?

Back 20

Front 21

Circuit symbols- What is a voltage symbol ?

Back 21

Front 22

Circuit symbols- What is a thermistor symbol ?

Back 22

Front 23

Circuit symbols- What is a LDR symbol ?

Back 23