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10

explain the first law of thermodynamics

the heat supplied to a system is used for doing work and changing the temperature (or internal energy) of the system.

10

meaning of thermodynamics

thermo - heat 

dynamics - motion

10

A crane engine uses 80 000J obtained from diesel burning. it spends 30 000J to lift container. What is the chsnge in internal energy? 

U = Q - W 

U = 80 000 - 30 000 

U = 50 000J

10

main particles of atom

proton electron and neutron 

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why do cars have exhaust pipes?

the exhaust system carries harmful gases like carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC) away from the engine and passenger compartment to ensure safety

20

is it better to have greater U or smaller U? why?

better to have smaller

because of efficiency

20

An engine burns 6 kg of fuel and produces 6*106 Joules of useful work in 10 minutes. 24*106 Joules goes to exhaust

what is the useful power of engine? 

E = P*t

P =E/t 

P = 6*106/600

P = 6*104W

20

An engine burns 6 kg of fuel and produces 6*106 Joules of useful work in 10 minutes. 24*106 Joules goes to exhaust

How many Joules does fuel give

Etotal = Euseful + Eexhaust

E = 24*106 + 6*106
E = 30 * 106J
20

An engine burns 6 kg of fuel and produces 6*106 Joules of useful work in 10 minutes. 24*106 Joules goes to exhaust

How many energy does 1 kg of fuel give?

Etotal/Q = mq 

q = E/q

q = 30*106/6

q = 5*106 J/kg

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types of processes and examples

reversible and irreversible 

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main sources of energy

fossil, biomass, nuclear, water, sun and wind

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explain the second law of thermodynamics

1) heat can’t flow from colder object towards hotter objects by itself

2) no heat machine can convert all heat into useful work

30

explain charding method grounding

charges flow by wire from object to ground

30

the smallest charge

electron -1.6*10-19C

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________ when charges shape the space around them forming a field that interacts with other charges

electric field

40
the magnitude of electric field of charge q at point P is 9*105N/C. what force does a charge of q1 = 1*10-6C experience if it if placed at point P?

F=qE

10-6*9*105 = 0.9N

40

determine the electric field at point P a distance 20cm form the negatively charged particle q = -4*10-6C

E=k|q|/r2

E = 9*109*4*10-6/0.04

E = 900 * 103 = 9*105N/C

40

what is electric potential?

the ratio of electric potential energy to the charge
40

Find the potential energy of a system of point charges of q1=20*10-6C and q2=-10*10-6C when they are 20cm apart

Ep = kqq/r 

Ep = 9*109 * (20*10-6)* (-10*10-6)/0.2 =-9J

40

parts of parallel capacitors

plates and wire

50
what is capacitor?

part of device which stores charges

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where we use capacitors

computer, phone, cameras

50

unit of capacitance

Farad [F]

50

A parallel plate capacitor of capacitace 4*10-6F, carries a charge of 60*10-6C. what if the potential difference between the plates of the capacitor?

C=q/U

U=q/C 

U = 60*10-6/5*10-6 = 15V

50

Electric field starts with _____ ends with ______

positive - negative

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