# SP10 Electricity and Circuits

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- Created by: AStarStudent2004
- Created on: 22-05-19 18:00

## SP10a Electric Circuits

**Nucleus**- includes**protons**, mass of 1 and charge of +1, and**neutrons**, mass of 1 and charge of 0.**Shells**- includes electrons, mass of**1/1835**and charge of -1.- Metals have one electron in the outer shell - weakly attracted to nucleus. Electrons can be easily removed, so many
**'free' electrons**. Voltage pushes the electrons arount the**circuit**. **Convectional current**- current flows**+ve terminal to -ve terminal**, opposite from electron flow.**Series circuit**-**one**route current can take.**Parallel circuit**- junctions allow current to take**different**routes.

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## SP10b Current and Potential Difference

**Current**- measured in units of**amperes**(amps, A), with an**ammeter.**- Current is
**conserved**- total amount of current is the**same**around the circuit. The total amount entering junction is the same leaving. **Potential difference/voltage**- measured in**volts**, using a**voltmeter**and is needed for electrons to flow.- The
**bigger**the voltage,**bigger**the current. - Voltage across all components
**add up**to give voltage produced by battery/cell.

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## SP10c Current, Charge and Energy

**Electric charge**- measured in**Coulombs (C)****Electron**charge -**-1.6 x 10^-19****Size of current**tells how much**charge flows**past each second.**Electic current**- rate of**flow**of**charge**(**electrons**).**Charge (C) = current (A) x time (s)/ Q = I x t****Energy transferred (J) = charge moved (C) x voltage (V)/ E = Q x V**

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## SP10d Resistance

**Resistance**- how**hard**it is for current to**flow**, measured in**ohms (Ω)**.**Voltage (V) - current (A) x resistance (Ω)/ V = I x R**- Resistors in
**series**- resistance is**increases**, pathway**harder**for current to flow. Voltage shared betweeen resistors**not**always**equal**. - Resistors in
**parallel**- total resistance**less**than indivdual as there's**more paths**for current.

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## SP10e More about Resistance

**Direct Proportion**- two variables change by**same percentage**(straigh-line through origin).- (When voltage change:)
**Fixed resistor**-**current**changes as**voltage**changes at**direct proportion**, resistance same. **Lamp**- voltage causes**current**to**flow**and it**heats**up lamp.**Bigger**the**voltage**,**more current**,**hotter**lamp. As it**heats**up -**resistance increases**(not direct proportion).**Diode**-**low**resistance if voltage in**1 direction**but**high**in**opposite**(current can**only**flow in 1 direction).**L**-**i**ght dependent resistor (LDR)**high**resistance in**dark**, resistance**decrease**as**light increases.****Thermistors**-**high**resistance in**low temps**, temp**increases**as resistance**decreases.**

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## SP10f Transferring energy

- All circuits have
**resistance**-**warm up**when there's a current (**heating effect**). - Current passes through
**resistor**- energy transferred by**heating**because**electrical work done**against**resistance**. **Heating effect**- useful in**heaters/kettle**. Not useful in a**computer/plugs**as useful energy is transferred from**circuit by heating**and**dissipated**into surroundings.**Lattice in resistor**- as electrons**flow**through lattice of vibrating ions, they**collide**with ions.**More collisions**, the**harder**it is to flow,**more resistance**. When they**collide**, they t**ransfer energy**to them.**Reducing resistance**- using wires of metals with**low resistance**.**Cooling metals**, so that lattice ions**not vibrating**as much.**Energy transferred (J) = current (A) x voltage (V) x time (S)/ E = I x V x t**

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## SP10g Power

**Power**-**energy transferred per second**,**Watts (W)**.**Power (W) = energy transferred (J) ÷ time (s)/ P = E ÷ t****Electrical power (W) = current (A) x voltage (V)/ P = I x V****Electrical power (W) = current² (A²) x resistance (Ω)/ P = I² x R**

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## SP10h Transferring Energy by Electricity

- Energy from
**battery**transfers by electricity to the**motor**, where it's transferred to store of**kinetic energy**in fan. Some energy transfers by**heating wires**, motor and surroundings.**All**energy will dissipate by heating, in the end. - Gloves contain wire with
**high resistance**. Energy from**battery**transfers by electricity to**wire**, where it's transferred by**heating**to store of**thermal energy**. The energy transfers to gloves and hand, and**dissipates**to surroundings. **National grid**- network of**wires**that carries electricity to homes.**Direct current**- a current flows in**one direction only**, the direction of movent of charge stays same.**Voltage - 230V****Alternating current**- current that changes direction**many times**each second. Voltage changes from peak voltage to zero (**50 Hertz**).**Average effect - 230V.**

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## SP10i Electrical Safety

**Earth Wire**- A safety wire to**stop**the appliance becoming**live.****Neutral Wire**- carries current**back**to the**source**and**completes circuit.****Live Wire**- has a voltage of**230V**and provides**current.****Fuse**- tube with thin wire that**melts**when current**exceeds**a certain value (**3A, 5A and 13A**),**stops current/breaks circuit**.- Fuses
**stops fire**from**overheating**wires, and**earth wire**stops current from**flowing**in you if there's a**fault**. - If
**live wire**touches a**metal**part, there's large current flowing to**earth**,**heats wire**and causes**fire.** **Circuit breakers**-**detect**change in current and**swithes off**supply. Can be**re-used**,**quick, saves lives**.**Fuse**has to be**replaced**, fues takes**time**, doesn't save you from**shock.**

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