Section 21 - Electricity and circuits - Current, potential difference, resistance, components and circuit devices

Question 1

What is current? Unit?

Unit for charge?

Answer 1

The rate of flow of electric charge, unit in ampere (A)

Charge unit - coulombs (C)

Question 2

What is potential difference (or voltage)? Unit?

Answer 2

The driving force that pushes the charge around, unit in volt (V)
Energy transferred per coulomb of charge

Question 3

What is resistance? Unit?

Answer 3

Anything that slows down current flow, unit in ohm (Ω)

Question 4

Formula for charge?

Answer 4

Charge (C) = current (A) x time (s)

Q = I x t

Question 5

Formula for energy transferred?

Answer 5

Energy transferred (J) = charge moved (C) x p.d. (V)
E = Q x V

Question 6

Formula for potential difference?

Answer 6

p.d. (V) = current (A) x resistance (Ω)

V = I x R

Question 7

Why does a resistor heat up when a current flows through a resistor?

Answer 7

The electrons collide with the ions in the lattice of resistor as they flow through it. This gives ions energy, which causes them to vibrate and heat up

Question 8

What happens to current when a resistor heats up?

Answer 8

Current decreases as it is harder for electrons to get through resistor

Question 9

What does an ammeter measure? Where should it be placed in a circuit?

Answer 9

Measures current (in amps) flowing through component. Can be put anywhere in main circuit but must be in series.

Question 10

What does a voltmeter measure? Where should it be placed in a circuit?

Answer 10

Measures p.d. across component. Must be placed in parallel with component under test

Question 11

What happens to current and resistance when a thermistor’s temperature increases?

Answer 11

Current through thermistor increases as resistance decreases

Question 12

What happens to current and resistance when a LDR’s light level gets brighter?

Answer 12

Current through LDR increases as resistance decreases

Question 13

What happens if you swap diodes and LED’s in the other direction?

Answer 13

Current cannot flow through diode anymore as current only flows in one direction

Question 14

What is an I-V graph like for resistors and wires?

Answer 14

Current is directly proportional to p.d.. Straight, positive gradient going through (0,0)

Question 15

What is an I-V graph like for filament lamp?

Answer 15

Increasing current increases temperature of filament, which makes resistance increase so I-V graph is curved.

Question 16

What is an I-V graph like for diodes?

Answer 16

Current will only flow in one direction through diode. It has very high resistance in opposite direction. Flat until y-axis where curved increase

Question 17

What is the resistance of a component like for linear components if the line goes through (0,0) on an I-V graph?

Answer 17

Resistance of component equals inverse of gradient of line, or 1 ÷ gradient