# (c) Energy and voltage in circuits

## 2.07 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

• Components (e.g. bulbs) may be switched on/off independently.
• If one component breaks, current can still flow through the other parts of the circuit.
• Bulbs maintain a similar brightness.

• Fewer wires, cheaper and easier to assemble.
• Uses less power

## 2.09 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how to investigate this experimentally

in the bellow diagram the red box could represent a wire, a bulb, a resistor or a diode.

By changing the resistance of the variable resistor the graphs are reproduced.  ## 2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs) with illumination and thermistors with temperature

LDR

As illumination increases, resistance decreases

Thermistor

As temperature increases, resistance decreases. ## 2.13 know and use the relationship between voltage, current and resistance: V = I × R

Potential difference (V) = Current (A) x Resistance (Ω) ## 2.15 know and use the relationship between charge, current and time: Q = I × t

Charge (C) = Current (A) x Time (s) ## 2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons

Electrons are negatively charged and free to flow in a metal so carry charge ## 2.20 know that: voltage is the energy transferred per unit charge passed and the volt is a joule per coulomb  Select a set of flashcards to study:

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Section 1: Principles of chemistry

a) States of matter

b) Atoms

c) Atomic structure

d) Relative formula masses and molar volumes of gases

e) Chemical formulae and chemical equations

f) Ionic compounds

g) Covalent substances

h) Metallic crystals

i) Electrolysis

Section 2: Chemistry of the elements

a) The Periodic Table

b) Group 1 elements: lithium, sodium and potassium

c) Group 7 elements: chlorine, bromine and iodine

d) Oxygen and oxides

e) Hydrogen and water

f) Reactivity series

g) Tests for ions and gases

Section 3: Organic chemistry

a) Introduction

b) Alkanes

c) Alkenes

d) Ethanol

Section 4: Physical chemistry

a) Acids, alkalis and salts

b) Energetics

c) Rates of reaction

d) Equilibria

Section 5: Chemistry in industry

a) Extraction and uses of metals

b) Crude oil

c) Synthetic polymers

d) The industrial manufacture of chemicals

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