STPM Physics Chapter 15 Direct Current Circuits

STPM PHYSICS CHAPTER 15 DIRECT CURRENT CIRCUITS

SMK SACRED HEART, SIBU 1.

Electromotive force (e.m.f.), E = energy supplied to each coulomb of charge that flows from the source.

E= =

Since its unit is V, from V =

V1 = V G I1 R1 = IG RG

E=

E = I (R + r) =1+

E= 2.

=

11. Potentiometer (When G = 0) Diagram

Itotal = I1 = IG =

=

=

Formula R=

Potential difference between two points V=

= =constant =

3.

Maximum current Imaximum = , r = internal resistance Due to presence of r , V < E, hence

4. 5.

Electrical power, P Series – parallel Type Maximum Series Voltage Parallel Current 6. Maximum power 2

P=I R=( 7.

V = E – Ir V = IR = =

P = IV = I2R =

= constant

Hence,

=

V = IR = = 2

) R , when R = r

= constant

Thus,

Kirchhoff’s first law: The algebraic sum of the currents at a junction of a circuit is zero. [ Principle of conservation of charge ]

=

Hence, =

= ,

∑ = 0 or Iin = Iout

=

Kirchhoff’s second law: In a closed loop, the algebraic sum of the e.m.f.s is equal to the products of current and resistance. [Principle of conservation of energy ] *Refer to Kirchhoff’s Law question analysis

=

, V1 = E

=

=1+

8.

9.

Potential and current divider Poetntial divider

Itotal = I1 = I2 =

=

=

10. Shunt and multiplier Shunt Resistor of lower resistance than that of galvanometer and is connected parallel to galvanometer

∑

=∑

Current divider

Vtotal = V1 = V2 Itotal R total = I1 R1 = I2 R2 Multiplier Resistor of high resistance connected in series with the galvanometer.

2 = new length when S1 is closed

=

=

= 12. Wheatstone bridge & Metre bridge If R and S are replaced by wires. Then: PQRS are resistance