dual core prcoessors only have one physical core?

Dual core is the general term for processors with two independent CPUs. Core 2 Duo is Intel's brand name for one of their dual core processors. It's akin to the difference between a compact car and a Honda Civic.

Core 2 Duo is a brand name by Intel. "Dual Core" is a generic description meaning two separate physical cores in one chip.

Np. There are Intel's Dual core(Intel D) processors too. I mean what is the difference between Intel dual core and core 2 duo?
I know what core 2 duo has two physical processors inside. but.....

Most of the confusion comes from the following...

Intel Pentium D
Intel Core Duo
Intel Core 2 Duo
Intel Pentium Dual-Core

You asked about Pentium D vs Core 2 Duo. The Pentium D is the earlier model. The Core 2 Duo is a much better model, better performance.

The Pentium Dual-Core is based on Core 2, but has less L2 Cache so its more affordable.

what about dual core only having one physical core and anotehr virtual core? lie?

Actually The Core 2 Duo processor has two parallel cores inside a single physical package and the two cores sharing their load. so, the core 2 duo processor is faster. But in dual core processor the two cores in Series and the both cores are working at same time. So it is much slower then core 2 duo processor. And also the multi-tusking performance also less in the dual core processor.